Proposal for a Detector of Photons with Zero Projection of... I. G. Savenko

Transcription

Proposal for a Detector of Photons with Zero Projection of Spin
I. G. Savenko
arXiv:1411.1881v1 [cond-mat.mes-hall] 7 Nov 2014
COMP Centre of Excellence at the Department of Applied Physics and Low Temperature Laboratory (OVLL),
Aalto University School of Science, P.O. Box 13500, FI-00076 Aalto, Finland
(Dated: November 10, 2014)
We suggest an indirect method of detection of photons with zero projection of spin mediated by
emission of terahertz photons. This terahertz source is based on a system of microcavity exciton
polaritons in the regime of polariton BEC formation where the cavity photons aquire an effective
mass being localised in the cavity and therefore receive the third spin degree of freedom. The optical
transitions can occur between two polariton ground states (based on the excitons e1-hh and e1-lh)
accompanied by the emission of terahertz radiation with controllable characteristics.
PACS numbers: 78.67.Pt,78.45.+h
It is commonly believed that photons may have only
two polarizations (we will refer to them as “spins” in
what follows), ±1 (or superpositions), being massless
particles, or more precisely, massless vector fields [1]. For
a massive field, however, it is always possible to find a
so-called “rest frame” where the spin is zero, which is one
of the milestones of the Field theory [2]. A photon has no
rest mass in a free space and therefore for the photon only
spin eigenfunction along the direction of propagation exists. However, when localized in the travel direction, a
photon acquires an effective mass, due to the fact that
its dispersion becomes quasi-parabolic [3],
~2 kk2
cq 2
c
2
kz + kk ≈ E0 +
.
~ω = ~ |k| = ~
n
n
2m∗
Here z is the direction of propagation and m∗ is the effective mass. A question arises: is it possible for a photon to
have zero projection of spin and, even more significant,
is it feasible to measure it or use?
In this manuscript we propose an indirect method of
detection of zero-spin photons and suggest a possible application of these results. (A direct measurement seems
impossible since zero-spin photons do not exist in free
space.) For this, we consider a system of exciton polaritons (later “polaritons”) in a semiconductor microcavity. These quasi-particles have hybrid light-matter nature and they result from the strong coupling regime in
the cavity. Usually, a polariton is formed when a photon interacts with a Wannier-Mott exciton, based on the
heavy hole (e1-hh exciton). Due to the fact that the electrons and holes are localized in the semiconductor quantum wells (QWs), the degeneracy between the light hole
(lh) and heavy hole branches of the valence band at k = 0
is lifted. Thus, the energy of the exciton e1-hh is usually
lower than the energy of the e1-lh exciton. Therefore,
the polaritons based on the excitons e1(±1/2)-hh(±3/2)
are usually created [4, 5]. They have finite lifetime since
photons leak through the cavity mirrors (DBRs), that is
why a constant pumping of the system is required for its
operation (see Fig. 1). This pumping, or excitation, can
be organized either optically (exposition) [6] or electri-
cally (current injection) [7]. In the latter case, which we
will focus on in current work, an electron-hole cloud is
created; later the carriers of charge form excitons which
start to (re)emit and (re)absorb photons in the cavity.
This way the exciton polaritons come into play.
It has been shown in a number of theoretical works that
such system can serve as a source of terahertz (THz) radiation [8–12] in the regime of polariton laser generation
(spontaneous emission from the quasi-condensate). THz
range still remains an uncovered region of electromagnetic spectrum: there still does not exist a solid state
source of THz radiation with satisfactory characteristics
[13, 14]. The main and fundamental objection to creating
such a source is small density of states of THz photons
resulting in small rate of spontaneous emission [15, 16].
However fortunately, the emission rate can be increased
by application of the Purcell effect if the emitter of THz is
placed in a cavity tuned at the THz mode [17, 18]. Moreover, the rate of spontaneous emission of THz photons
can be additionally increased by the bosonic stimulation
if the radiative transition occurs between the condensate
states. For instance, it could be a transition between the
upper and lower polariton branches’ ground states in the
microcavity. However, radiative transition between such
modes (originated from the exciton and cavity modes)
is forbidden due to the selection rules (since initial and
final polariton states correspond to the same exciton and
thus have equal parity). The described radiative transition becomes possible if one of the states participating in
the photoemission process is hybridized with an exciton
state of different parity by an applied electric field [8].
In the configuration which we propose in this work, the
radiative transition can be achieved in a straighter way
though.
We consider a planar quantum microcavity based on
an InGaAlAs alloy in the strong coupling regime, when
the exciton polaritons are formed on both the heavy- and
light-hole excitons. The formation of polaritons based on
the light hole has no fundamental objections since it does
not violate the selection rules and, moreover, creation of
the lh excitons has been recently demonstrated experi-
Large Magnetic Shielding Factor Measured by
Nonlinear Magneto-optical Rotation
arXiv:1411.1962v1 [physics.ins-det] 7 Nov 2014
J.W. Martina,b,∗, R.R. Mammeia,b , W. Klassena,b , C. Cerasania , T. Andalibb ,
C.P. Bidinostia,b , M. Langb , D. Ostapchuka
a Physics
Department, The University of Winnipeg, 515 Portage Avenue, Winnipeg, MB,
R3B 2E9, Canada
b Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB R3T 2N2,
Canada
Abstract
A passive magnetic shield was designed and constructed for magnetometer tests
for the future neutron electric dipole moment experiment at TRIUMF. The axial
shielding factor of the magnetic shield was measured using a magnetometer
based on non-linear magneto-optical rotation of the plane of polarized laser
light upon passage through a paraffin-coated vapour cell containing natural
Rb at room temperature. The laser was tuned to the Rb D1 line, near the
85
Rb F = 2 → 2, 3 transition. The shielding factor was measured by applying
an axial field externally and measuring the magnetic field internally using the
magnetometer. The axial shielding factor was determined to be (1.3±0.1)×107 ,
from an applied axial field of 1.45 µT in the background of Earth’s magnetic
field.
Keywords: Magnetometer, Magnetic Shielding, Neutron Electric Dipole
Moment, Nonlinear Magneto-Optical Rotation
1. Introduction
The next generation of neutron electric dipole moment (EDM) experiments
aim to measure the EDM dn with proposed precision δdn . 10−27 e-cm [1, 2, 3,
∗ Corresponding
author
Email address: [email protected] (J.W. Martin)
Preprint submitted to Nuclear Instruments and Methods in Physics Research ANovember 10, 2014
Upgrade of the ALICE Inner Tracking System
Felix Reidt for the ALICE collaboration∗†
CERN, 1210 Geneva 23, Switzerland and
Physikalisches Institut, Ruprecht-Karls-Universitaet Heidelberg,
Im Neuenheimer Feld 226, 69120 Heidelberg, Germany
E-mail: [email protected]
During the Long Shutdown 2 (LS2) of the LHC in 2018/2019, the ALICE experiment plans the
installation of a novel Inner Tracking System (ITS). The upgraded detector will fully replace
the current ITS having six layers by seven layers of Monolithic Active Pixel Sensors (MAPS).
The upgraded ITS will have significantly improved tracking and vertexing capabilities, as well as
readout rate to cope with the expected increased Pb-Pb luminosity in LHC. The choice of MAPS
has been driven by the specific requirements of ALICE as a heavy ion experiment dealing with
rare probes at low pT . This leads to stringent requirements on the material budget of 0.3 % X/X0
per layer for the three innermost layers. Furthermore, the detector will see large hit densities of
∼ 19 cm−2 /event on average for minimum-bias events in the inner most layer and has to stand
moderate radiation loads of 700 kRad TID and 1 × 1013 1 MeV neq /cm2 NIEL at maximum. The
MAPS detectors are manufactured using the TowerJazz 0.18 µm CMOS Imaging Sensor process
on wafers with a high-resistivity epitaxial layer.
This contribution summarises the recent R&D activities and focuses on results on the large-scale
pixel sensor prototypes.
The 23rd International Workshop on Vertex Detectors
15-19 September 2014
Macha Lake, The Czech Republic
∗ Speaker.
† My work is supported by the Wolfgang-Gentner programme of the Bundesministerium für Bildung und Forschung
(BMBF).
c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
http://pos.sissa.it/
Felix Reidt for the ALICE collaboration
Upgrade of the ALICE Inner Tracking System
1. Introduction
ALICE (A Large Ion Collider Experiment) [1] is a general-purpose, heavy-ion experiment
at the CERN LHC. It’s main goal is to study the physics properties of the Quark-Gluon Plasma
(QGP). During the Long Shutdown 2 (LS2) of the LHC in 2018/2019, ALICE will undergo a major
upgrade in order to significantly enhance its physics capabilities, in particular for high precision
measurements of rare probes at low transverse momenta.
1.1 ALICE Upgrade
The ALICE upgrade programme during LS2 is based on a combination of detector upgrades
improving their physics performance and preparing them for a significant luminosity increase to
L = 6 × 1027 cm−2 s−1 for nucleus-nucleus (A-A) collisions. The increased luminosity will lead to
a Pb-Pb interaction rate of about 50 kHz. The study of rare probes at low transverse momenta in
heavy-ion collisions make triggering impossible due to the large combinatorial background. Thus,
the upgraded experimental apparatus is designed to readout all Pb-Pb interactions, accumulating
events corresponding to an integrated luminosity of more than 10 nb−1 . This minimum bias data
sample will provide an increase in terms of statistics by about a factor 100 with respect to the
programme until LS2. The upgraded detector will provide improved vertexing and tracking capabilities at low pT . In summary, the detector upgrade [2] consists of the following sub-system
upgrades:
• Reduction of the beam pipe radius from 29.8 mm to 19.8 mm allowing the inner layer of the
central barrel silicon tracker being moved closer to the interaction point.
• New high-resolution, high-granularity, low material budget silicon trackers:
– Inner Tracking System (ITS) [3] covering mid-rapidity.
– Muon Forward Tracker (MFT) [4] covering forward rapidity.
• The wire chambers of the Time Projection Chamber (TPC) will be replaced by GEM detectors and new electronics will be installed in order to allow for a continuous readout [5].
• Upgrade of the forward trigger detectors and the Zero Degree Calorimeter [6].
• Upgrade of the readout electronics of the Transition Radiation Detector (TRD), Time-OfFlight (TOF) detector, PHOS and Muon Spectrometer for high rate operation.
• Upgrade of online and offline systems (O2 project) [2] in order to cope with the expected
data volume.
2. ALICE ITS Upgrade
The main goals of the ITS upgrade are to achieve an improved reconstruction of the primary
vertex as well as decay vertices originating from heavy-flavour hadrons and an improved performance for detection of low-momentum particles. The design objectives are to improve the impact
parameter resolution by a factor of 3 and 5 in the rϕ and z coordinate, respectively, at a transverse
2
Preprint typeset in JINST style - HYPER VERSION
Potential of Thin Films for use in Charged Particle
Tracking Detectors
J. Metcalfea∗, I. Mejiab , J. Murphyb , M. Quevedob , L. Smithb , J. Alvaradoc , B. Gnadeb ,
and H. Takaia
a Brookhaven
National Laboratory,
PO Box 5000, Upton, NY 11973, USA
b University of Texas, Dallas,
800 W Campbell Rd, Richardson, TX 75080, USA
c Benemerita
´
Universidad Autonoma
´
de Puebla,
Calle 4 Sur 104, Centro Historico
72000 Heroica Puebla de Zaragoza, PUE, Mexico
A BSTRACT: Thin Film technology has widespread applications in everyday electronics, notably
Liquid Crystal Display screens, solar cells, and organic light emitting diodes. We explore the
potential of this technology as charged particle radiation tracking detectors for use in High Energy
Physics experiments such as those at the Large Hadron Collider or the Relativistic Heavy Ion
Collider. Through modern fabrication techniques, a host of semiconductor materials are available
to construct thin, flexible detectors with integrated electronics with pixel sizes on the order of a few
microns. We review the material properties of promising candidates, discuss the potential benefits
and challenges associated with this technology, and review previously demonstrated applicability
as a neutron detector.
K EYWORDS : Thin Film Diode, Thin Film Transistor; Tracking Detector; High Energy Physics.
∗ Corresponding
author.
Nuclear Physics B
Proceedings
Supplement
Nuclear Physics B Proceedings Supplement 00 (2014) 1–6
Probing CP violation in B0s → KS0 π+ π− decays
Tim Gershon, Thomas Latham and Rafael Silva Coutinho
arXiv:1411.2018v1 [hep-ph] 7 Nov 2014
Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
Abstract
The three-body charmless hadronic decay B0s → KS0 π+ π− provides a number of novel possibilities to search for CP
violation effects and test the Standard Model of particle physics. These include fits to the Dalitz-plot distributions
of the decay-time-integrated final state, decay-time-dependent (but without initial state flavour tagging) fits to the
Dalitz-plot distribution, as well as full decay-time-dependent and flavour tagged fits. The relative sensitivities of these
different approaches are investigated.
Keywords: CP violation, b-hadron decays, Dalitz-plot analysis
1. Introduction
The search for a new source of CP violation in addition to that predicted by the CKM matrix [1, 2] is
among the main goals of current particle physics research. In the quark sector, a number of important tests
have been performed by experiments such as BaBar,
Belle and LHCb [3–7]. This line of investigation will
be continued by Belle II [8] and the upgraded LHCb
experiment [9, 10].
One of the most interesting approaches to search for
new sources of CP violation is by studying the decaytime distribution of neutral B meson decays to hadronic
final states mediated by the loop (“penguin”) b → s
amplitude. As-yet undiscovered particles can contribute
in the loops and cause the observables to deviate from
their expected values in the Standard Model (SM) [11–
14]. Studies of B0 decays to φKS0 , η0 KS0 , KS0 KS0 KS0 and
various other final states have been performed for this
reason. The latest results are consistent with the SM
predictions, but improved measurements are needed to
be sensitive to small deviations.
Experience from previous experiments has shown
that full decay-time-dependent Dalitz-plot analysis of
a three-body decay (for example B0 → KS0 π+ π− ) is
more sensitive than a “quasi-two-body” approach (in
this example, considering only the KS0 ρ0 contribution).
This is particularly notable in the case that broad resonances contribute, since interference causes effects
to which quasi-two-body approaches have no sensitivity [15–17]. Several methods have been proposed to
exploit such interferences in b → s transitions to allow determination of underlying parameters such as the
CKM phase γ with reduced theoretical uncertainty [18–
22]. Full decay-time-dependent Dalitz-plot analyses of
B0 → KS0 π+ π− [23, 24] and B0 → KS0 K + K − [25, 26]
have been performed by BaBar and Belle, but similar
studies of B0s meson decays have not yet been possible.
First results from LHCb on decays of the B0s meson
via hadronic b → s amplitudes have, however, recently
become available. Decay-time-dependent analyses of
B0s → K + K − [27] and B0s → φφ [28] have already been
performed. The first observations of B0s → KS0 K ± π∓ and
B0s → KS0 π+ π− have also been reported [29], including
information on contributing K ∗ resonances [30], suggesting that it will be possible to study CP violation in
these modes in the future.
One interesting feature of the B0s → KS0 π+ π− decays is
that an asymmetry in the time-integrated yields across
the mirror line of the Dalitz plot is a signature of CP
violation [31–33]. This can be exploited to search for
CP asymmetry with either model-independent or modeldependent approaches. Another important aspect of the
Indirect Detection of WIMP Dark Matter: a compact review
Jan Conrad , Oskar Klein Centre, Physics Department, Stockholm University, Albanova,
SE-10691 Stockholm, Sweden
arXiv:1411.1925v1 [hep-ph] 7 Nov 2014
Abstract
Indirect detection of dark matter particles, i.e. the detection of annihilation or
decay products of Weakly Interacting Massive Particles, has entered a pivotal phase as
experiments reach sensitivities that probe the most interesting parameter space. This
period is naturally accompanied by claims of detection. In this contribution I discuss
and compare different probes (gamma-rays, neutrinos and charged cosmic rays) and
review the status and prospects of constraints and recent detection claims.
To appear in the proceedings of the Interplay between Particle and Astroparticle Physics workshop,
18 – 22 August, 2014, held at Queen Mary University of London, UK.
1
Introduction
Cosmological observations now proof beyond reasonable doubts that around 85 % of the
matter component of the Universe is comprised of new type of matter, dubbed dark matter
(DM), see e.g. [1], consisting of particle(s) not currently part of the standard model. The
currently most popular, almost paradigmatic, candidate is a weakly interacting massive
particle (WIMP), i.e. a particle with weak interactions and masses roughly above the mass
of the proton. The reason for this paradigmatic status of the WIMP is that thermal WIMP
production in the big bang, whose processes are well gauged by the observations of light
elements, predict a global DM abundance within one dex of the observed one (e.g. [2]).
A result often called the “WIMP miracle”. There are three ways to try to find WIMPs.
Attempts to produce WIMPs are undertaken at the Large Hadron Collider, especially anticipating results of the new data at 14 TeV center of mass energy. WIMPs scattering of
deep underground low background detectors (e.g. [3]) is dubbed direct detection. Finally,
the approach discussed here, is to observe that WIMPs might annihilate (or decay) in dense
region of the Universe to yield standard model particles, in particular gamma rays, charged
leptons and neutrinos. For gamma rays and neutrinos, that essentially travel through space
undisturbed, the resulting flux is given by:
dR
= P · J(∆Ω)
dt dA dE
(1)
with R being the number of particles and P and J defined as:
P =
dNγi
hσann vi X
·
BR
i
2m2χ
dEi
i
1
(2)
CAFPE-185/14
CERN-PH-TH-2014-216
DESY 14-213
SISSA 60/2014/FISI
UG-FT-315/14
The Elusive Gluon
Mikael Chala1,2 , José Juknevich3,4 , Gilad Perez5
and José Santiago1,6
arXiv:1411.1771v1 [hep-ph] 6 Nov 2014
1
CAFPE and Departamento de Física Teórica y del Cosmos,
Universidad de Granada, E-18071 Granada, Spain
2
DESY, Notkestrasse 85, 22607 Hamburg, Germany
3
SISSA/ISAS, I-34136 Trieste, Italy
4
INFN - Sezione di Trieste, 34151 Trieste, Italy
5
Department of Particle Physics and Astrophysics,
Weizmann Institute of Science, Rehovot 76100, Israel
6
CERN, Theory Division, CH1211 Geneva 23, Switzerland
Abstract
We study the phenomenology of vector resonances in the context of natural composite Higgs models. A mild hierarchy between the fermionic partners and the vector
resonances can be expected in these models based on the following arguments. Both direct and indirect (electroweak and flavor precision) constraints on fermionic partners are
milder than the ones on spin one resonances. Also the naturalness pressure coming from
the top partners is stronger than that induced by the gauge partners. This observation
implies that the search strategy for vector resonances at the LHC needs to be modified.
In particular, we point out the importance of heavy gluon decays (or other vector resonances) to top partner pairs that were overlooked in previous experimental searches
at the LHC. These searches focused on simplified benchmark models in which the only
new particle beyond the Standard Model was the heavy gluon. It turns out that, when
kinematically allowed, such heavy-heavy decays make the heavy gluon elusive, and the
bounds on its mass can be up to 2 TeV milder than in the simpler models considered so
far for the LHC14. We discuss the origin of this difference and prospects for dedicated
searches.
YITP-SB-14-36
Projections for Dark Photon Searches at Mu3e
Bertrand Echenard,1, ∗ Rouven Essig,2, † and Yi-Ming Zhong2, ‡
2
1
California Institute of Technology, Pasadena, California 91125
C.N. Yang Institute for Theoretical Physics, Stony Brook University, Stony Brook, NY 11794
We show that dark photons (A0 ) with masses ∼ 10 − 80 MeV can be probed in the decay µ+ →
e νe ν¯µ A0 , A0 → e+ e− , with the upcoming Mu3e experiment at the Paul Scherrer Institute (PSI)
in Switzerland. With an expected 1015 (5.5 × 1016 ) muon decays in 2015–2016 (2018 and
beyond),ee
⌫⌫ee
Mu3e has the exciting opportunity to probe a substantial fraction of currently unexplored
dark +
0 −8 ). No
ee+
photon parameter space, probing kinetic-mixing parameter, , as low as 2 ∼ 10−7A0(10
A
+
modifications of the existing Mu3e setup are required.
+,⇤
e+
W +,⇤
+
+
µ
µ+
arXiv:1411.1770v1 [hep-ph] 6 Nov 2014
I.
⌫⌫¯¯⌫µµe
INTRODUCTION
There are only a few ways in which new particles and
forces below the weak-scale can interact with the standard model (SM) particles and have remained undetected
thus far. Among the simplest possibilities is the existence
of a light, massive vector boson called a dark photon (A0 ).
A substantial effort is underway to search for a dark photon with a variety of experiments. In this paper, we show
that the upcoming Mu3e experiment at the Paul Scherrer Institute (PSI) in Switzerland is also sensitive to dark
photons. Using an unprecedented number of muon decays1 in their search for the lepton flavor violating decay µ+ → e+ e− e+ , Mu3e can also search for the decay
µ+ → e+ νe ν¯µ A0 , A0 → e+ e− shown in Fig. 1. This allows
them to probe currently unexplored regions of the dark
photon parameter space. We note that while our focus
will be on vector bosons (the dark photon), other particles that couple to electrons and/or muons and decay to
an e+ e− pair could also be probed with Mu3e.
The dark photon is the mediator of a new, broken
U(1)D gauge group and appears in many theoretical scenarios, see e.g. [1–3] and references therein. It can interact with ordinary matter through “kinetic mixing” [4–6]
with the SM hypercharge, U(1)Y , gauge boson. At low
energies, the dominant effect is a mixing of the U(1)D
with the SM photon, U(1)EM , as described with the Lagrangian
0 µν 1 0 0µν 1 2 0 0µ
F − Fµν F
+ mA0 Aµ A . (1)
L = LSM − Fµν
2
4
2
Here LSM is the SM Lagrangian, is the kinetic mixing parameter, F 0µν (F µν ) is the U(1)D (U(1)EM ) field
strength, and mA0 is the dark photon mass (the mechanism for generating this mass is not important for our
purposes). The mixing between the dark photon and
the SM photon leads to an -suppressed coupling of the
µ
dark photon to the electromagnetic current, JEM
, i.e., to
∗ [email protected]
† [email protected]
‡ [email protected]
1
e
W
“Muon” refers to µ+ in this paper.
e
e+
A0
e+
W +,⇤
µ+
⌫¯µ
+
µ+
µ
µ+
ee
+
ee+
A00
A
+,⇤
W +,⇤
W
e
e+
A0
W +,⇤
W +,⇤
µ
+
+
ee+
⌫⌫ee
W +,⇤
A0
⌫¯µ
µ
⌫¯⌫e¯µ+
⌫e
e+
⌫e
e⌫¯µ
e+
FIG. 1: Feynman diagrams for (on-shell) dark photon production in muon decays, µ+ → e+ νe ν¯µ A0 , A0 → e− e+ .
quarks and charged leptons,
µ
L ⊃ e A0µ JEM
.
(2)
The two relevant parameters of the model are the kinetic
mixing parameter and the dark photon mass. The coupling in Eq. (2) allows the dark photon to be probed with
a wide range of experiments, see e.g. [1–3] for a recent
review and references. We do not consider the addition
of other low-mass particles to this model.
Theoretically, the values of the kinetic mixing and the
dark photon mass can take on a wide range of values.
However, much attention has recently been focused on
the MeV–GeV mass range. In this mass range, the dark
photon could explain the ∼ 3.6σ discrepancy between the
observed and SM value of the muon anomalous magnetic
moment (aµ ≡ gµ − 2, where gµ is the muon’s gyromagnetic ratio) [7–9] and offer an explanation for various dark
1
matter related anomalies through dark matter-dark1photon interactions [10–13]. Moreover, a dark photon mass
1
SNSN-XXX-YY
November 10, 2014
arXiv:1411.1981v1 [hep-ex] 7 Nov 2014
Fermionic decays of SM Higgs
Andrey Pozdnyakov
on behalf of the ATLAS and CMS collaborations
Department of Physics and Astronamy
Northwestern University, Evanston, IL, USA
In this document I present an overview of the recent results published
by ATLAS and CMS collaborations on the searches for SM Higgs boson
decay to fermions. The document summarizes the status of the analyses
up
√ to September of 2014 and contains the results of pp collision Data at
s =7 and 8 TeV. Searches for H → τ τ , H → bb, H → µµ and ttH
processes are presented.
PRESENTED AT
XXXIV Physics in Collision Symposium
Bloomington, Indiana, September 16–20, 2014
1
Introduction
The existence of the scalar boson with mass of 125 GeV has been established. The
properties of this new particle thus far are consistent with the standard model (SM)
Higgs boson. Decay modes for its discovery, H → ZZ/W W and H → γγ, provide
an indirect evidence for Higgs coupling to top quark due to its production in gluongluon fusion process (Fig. 1). Nevertheless a direct evidence for its decay to fermions
is crucial in order to uncover the true nature of the new particle. Standard Model
predicts that the coupling of the Higgs to fermions is proportional to the mass of the
fermion, hence one expects larger branching fraction of the decay to heavier leptons.
For example for a 125 GeV Higgs SM predicts B(H → bb) = 58 %, B(H → τ τ ) = 6 %.
In proton-proton collisions at LHC leading Higgs boson production mechanisms
are (Fig.√1): gluon-gluon fusion (ggF) – about 88% for SM Higgs with mH = 125
GeV at S = 8 TeV; Vector Boson Fusion (VBF) – 7%; associated production with
a Z or W boson (VH) – 5%; and a tt¯ fusion (ttH) – 0.4%.
Even though ggF process dominates, there are experimental advantages of VBF
and VH modes: tagging events with extra particles and reducing the backgrounds.
In VH production the tag is based on the leptonic decays of the Z/W bosons: missing transverse energy from neutrinos (ETmiss ) and/or leptons – W(`ν)H, Z(``)H and
Z(νν)H. Let me note the branching ratios of those decays: B(W → `ν) ≈ 10% per
lepton, B(Z → ``) ≈ 3.4%, B(Z → νν) ≈ 20%.
Typical VBF tag requires an event with two jets with mjj > 500 GeV and
|ηj1 − ηj2 | > 3.5.
This Note summarizes recent results released by ATLAS and CMS √
experiments
up to September of 2014.
pp Data sets at s = 7 TeV
√ It includes analyses of the
−1
−1
with Lint ≈ 5f b and s = 8 TeV with Lint ≈ 20f b .
2
H → ττ
The search for H → τ τ decay is challenging experimentally due to several reasons:
(1) reconstruction of the ETmiss from neutrinos, which is difficult at hadronic colliders; (2) jet reconstruction and energy resolution in hadronic final states; (3) large
irreducible background from Z → τ τ process.
In addition the analysis complicates by three different final states due to decay
modes of the taus: H → τlep τlep (12%), H → τlep τhad (46%), H → τhad τhad (42%).
Reconstruction of the Higgs boson candidate mass, mτ τ , from the visible decay
products of the τ -lepton is one of the key ingredients of the analysis. Both ATLAS and CMS accomplish this with similar methods: ATLAS makes use of Missing
Mass Calculator algorithm [2], while CMS does matrix element Likelihood Function
minimization [3]. See Fig. 2 for the validation of this procedure from CMS.
1
arXiv:1411.1941v1 [hep-ex] 7 Nov 2014
EPJ Web of Conferences will be set by the publisher
DOI: will be set by the publisher
© Owned by the authors, published by EDP Sciences, 2014
Light (Hyper-)Nuclei production at the LHC measured with ALICE
Francesco Barile for the ALICE Collaboration1 , a
1
Università degli Studi di Bari and INFN Bari
Abstract. The high center-of-mass energies delivered by the LHC during the last three
years of operation led to accumulate a significant statistics of light (hyper-)nuclei in pp,
p–Pb and Pb–Pb collisions. The ALICE apparatus allows for the detection of these rarely
produced particles over a wide momentum range thanks to its excellent vertexing, tracking and particle identification capabilities. The last is based on the specific energy loss
in the Time Projection Chamber and the velocity measurement with the Time-Of-Flight
detector. The Cherenkov technique, exploited by a small acceptance detector (HMPID),
has also been used for the most central Pb–Pb collisions to identify (anti-)deuterons at
intermediate transverse momentum.
Results on the production of stable nuclei and anti-nuclei in pp, p–Pb and Pb–Pb collisions are presented. Hypernuclei production rates in Pb–Pb are also described, together
with a measurement of the hypertriton lifetime. The results are compared with the predictions from thermal and coalescence models. Moreover the results on the search for
weakly-decaying light exotic states, such as the ΛΛ (H-dibaryon) and the Λ-neutron
bound states are discussed.
1 Introduction
Collisions of ultra-relativistic heavy ions provide a unique experimental condition to produce nuclei and hypernuclei thanks to the huge amount of energy deposited into a volume much larger than
in pp collisions. The measurements presented here, have been performed in Pb–Pb collisions at
√
√
sNN = 2.76 TeV as a function of collision centrality and in p–Pb collisions at sNN = 5.02 TeV
as a function of charged-particle multiplicity.
The unique particle identification capabilities of the ALICE detector [1] system is suited to
measure nuclei and hypernuclei and for the search of exotic states like Λn bound states and the
H-dibaryon. The production mechanisms of these particles are typically discussed within two
approaches: the statistical thermal model and the coalescence model. In the thermal model [2–4]
the chemical freeze-out temperature T chem acts as the key parameter at LHC energies. The strong
sensitivity of the nuclei production to the choice of T chem is caused by the large mass m and the exponential dependence of the yield given by the factor exp(-m/T chem ). In the coalescence model, nuclei
are formed by protons and neutrons which are nearby in space and exhibit similar velocities [5, 6]. A
quantitative description of this process, applied to many collision systems at various energies [7–14],
is typically based on the coalescence parameter BA (see Section 3). The two mechanisms give very
a e-mail: [email protected]
SUSY searches at CMS
Alessandro Gaz, University of Colorado
On the behalf of the CMS Collaboration.
arXiv:1411.1886v1 [hep-ex] 7 Nov 2014
1
Introduction
The recent discovery of the Higgs boson [1] constitutes a magnificent triumph for Particle
Physics, but the existence of such elusive particle also poses difficult challenges for the field.
The mass of the Higgs boson, not protected by any symmetry, receives quantum corrections
from physics at higher scales; these corrections, unless some miraculous fine tuning of the
parameters is in place, are expected to raise the mass of the Higgs Boson to a value orders
of magnitude higher than the ∼ 126 GeV that we have observed.
One of the most popular theories that have been proposed to solve this Hierarchy Problem is that of Supersymmetry (SUSY), which postulates the existence, for each particle of
the Standard Model (SM), of a supersymmetric partner with spin that differs by 1/2 unity
from that of the SM particle. The existence of these fermion-boson pairs provides a cancellation mechanism for the corrections of the Higgs mass that greatly reduces the need for
a fine tuning of the parameters. In a natural scenario, one in which there is only minimal
need for fine tuning, the masses of the partners of the t− and b−quarks, of the gluon, and
of the Higgs bosons are expected to be relatively low, not much above the 1 TeV threshold
(see e.g. [2]).
The search for a light t˜ has been one of the keynotes of the early SUSY searches at the
LHC, which focused on t˜ pair production with t˜ → tχ
˜01 as dominant decay channel. These
analyses (see e.g. [3]) already provide tight constraints for the Natural SUSY paradigm, but
have little sensitivity in particular regions of the phase space in which light t˜ pairs could
still be allowed. One such example is the region in which mt˜ − mχ ∼ mt ; for this case the
stop pair production would not be experimentally distinguishable from the SM tt events.
Dedicated analyses to cover for these blind regions of the classic t˜ searches have thus been
developed and some will be presented here.
In R−parity conserving scenarios, the Lightest Supersymmetric Particle (LSP) is stable
and neutral and thus it constitutes a viable candidate for the Dark Matter in the Universe.
In this contributions we focus on these R−parity conserving scenarios: the stable (and
neutral) LSP does not interact with the detector, thus producing sizable missing transverse
miss ). The results of the different searches are interpreted both using full realistic
energy (ET
models (pMSSM, cMSSM, mSugra, ... ) and Simplified Models, in which only few specific
production and decay processes for the SUSY particles are considered. Most of the attention
in the last two years has shifted towards the interpretation of SUSY results in terms of
Simplified Models.
1
Indirect constraints on New Physics from the B-factories
Alessandro Gaz, University of Colorado
arXiv:1411.1882v1 [hep-ex] 7 Nov 2014
On the behalf of the BABAR and Belle Collaborations.
1
Introduction
The existence of New Physics particles, with masses that can be orders of magnitude higher
than the scale of the Electroweak Symmetry breaking, can be probed by performing precision
measurements of physics phenomena at a much lower energy scale.
The decays of B and D mesons are an excellent example of relatively low energy phenomena that can be sensitive to New Physics scales at the TeV region or above, thanks to
the large amount of data collected by the BABAR and Belle detectors at the PEP-II and
KEKB accelerator facilities.
It is expected that New Physics effects will be revealed in decays that proceed through
loop or box diagrams, and thus are suppressed in the Standard Model (SM), so that exotic
particles can enter these loops and shift the value of some of the observables from the
value predicted by the SM. New Physics effects could also be observed at tree level in the
hypothesis of the existence of a Higgs-like particle, whose coupling to SM particles depends
on the mass of the latter. In this case violations of Lepton Universality could be observed.
In this contribution, I present some recent results obtained by the BABAR and Belle Collaborations, and briefly discuss their implications for the indirect searches for New Physics.
2
The BABAR and Belle Detectors at the PEP-II and KEKB
Colliders
The BABAR and Belle detectors, located at the PEP-II (US) and KEKB (Japan) e+ e−
colliders respectively, have been designed for precision studies (particularly CP -violation
phenomena) of the decays of B- and D-mesons, τ leptons, and quarkonium, and for the
measurement of low-energy cross-sections of light unflavored particles. The physics capabilities (similar for the two detectors) include good hermeticity, high tracking efficiency and
momentum resolution, excellent vertexing resolution, high particle identification capabilities (particularly for the K − π separation), good energy resolution of neutral particles in
the energy range of 20 MeV to a few GeV, and high-performance in muon reconstruction
and identification.
The data taking began in 1999 and lasted until 2008 (for BABAR) and 2011 (for Belle).
Most of the data have been collected at a center of mass energy corresponding to the mass
1
November 10, 2014
arXiv:1411.1873v1 [hep-ex] 7 Nov 2014
Review of direct CP violation in two and three body B decays
at LHCb
Marc Grabalosa G´
andara1
LPC - Clermont Ferrand, CNRS, France
Charmless B hadrons decays offer rich opportunities to test the Standard Model. CP violation in charmless charged two-body and three-body
B decays provides ways to measure the CKM angle γ and to search for
New Physics. Also, vector-vector final states provide additional interesting observables. Hereby, we present the latest LHCb results on hadronic
charmless B decays putting emphasis on the direct CP violation measurements.
PRESENTED AT
8th International Workshop on the CKM Unitarity Triangle
(CKM 2014)
Vienna, Austria, September 8-12, 2014
1
1
On behalf of the LHCb Collaboration.
Introduction
Charmless b-hadron decays are a testing ground for the Standard Model as they have
contributions from Tree and Penguin diagrams and CP violation may arise from the
interference of both. In particular, the measurement of CP violation observables,
as well as branching ratio measurements, can lead to an improvement of the CKM
matrix elements. Here, we report the latest analysis performed on charmless B decays
by the LHCb detector [1].
2
0
CP violation in the charmless B(s)
→ K ±π∓
The B 0 → K ± π ∓ and Bs0 → π ± K ∓ decays can be used for the measurement of direct
CP violation by looking at the so-called CP asymmetry which can be defined looking
at the decay rates of the self-tagged modes as
0
ACP (B 0 → K + π − ) =
Γ(B → K − π + ) − Γ(B 0 → K + π − )
0
Γ(B → K − π + ) + Γ(B 0 → K + π − )
.
This asymmetry has been recently measured by the LHCb with 1 fb−1 of data
at center-of-mass energy 7 TeV [2]. After an efficient selection which takes into
account different optimizations for B 0 and Bs0 modes, the signal candidates are used
to measure the raw asymmetry which are later corrected for detection and production
asymmetries. Their measured CP asymmetries are
ACP (B 0 → K + π − ) = −0.080 ± 0.007(stat) ± 0.003(syst)
ACP (Bs0 → π + K − )
=
0.27 ± 0.04(stat) ± 0.01(syst)
being the most precise measurement (10.5σ) of CP violation in B 0 → K ± π ∓ and the
first observation (6.5σ) of CP violation in Bs0 decays.
3
CP violation on B ± → h±h+h−
Charmless three-body decays are dominated by processes involving intermediate resonances, and thus, rich interference patterns may arise. After the first evidence of
CP violation in B ± → h± h+ h− [3, 4], an update of the analysis is performed with
3 fb−1 [5] with the aim of measuring CP violation inclusively but also in the phase
space by looking for CP violation asymmetries in local regions of the Dalitz plot.
New selection criteria including a multivariate technique and new particle identification variables are used. The signal candidates are extracted from an unbinned maximum likelihood fit to the mass spectra of the selected candidates: B ± → K ± π + π − ,
B ± → K ± K + K − , B ± → π ± π + π − and B ± → π ± K + K − . After including the effects
1
T Violation in K-Meson Decays
Klaus R. Schubert,
Technische Universit¨
at Dresden and Johannes Gutenberg-Universit¨
at Mainz
arXiv:1411.1862v1 [hep-ex] 7 Nov 2014
To appear in the proceedings of the 50 years of CP violation conference, 10 – 11 July, 2014, held at
Queen Mary University of London, UK.
1
Introduction
The first reported meson was a charged Kaon, observed with a cloud chamber in cosmic
rays in 1944 [1], three years before the discovery of the charged pion [2]. The neutral Kaon
was also discovered in 1947 [3]. In 1955, Gell-Mann and Pais [4] predicted that the K 0
is a two-state particle with a non-exponential decay law. This was confirmed in 1956 [5]
with 20 K 0 decays showing a life time at least 10 times longer than that of the dominant
K 0 → π + π − decays. In the same year, Lee and Yang [6] concluded that weak decays violate
P symmetry since the charged Kaon decays into 2π and 3π states with opposite parity. P
violation was confirmed in two experiments [7, 8] one year later. In 1964, Chistenson et
al. [9] discovered that also CP symmetry is violated, either in decays of the long-living K 0
state KL (CP=-1) into π + π − or in K 0 K 0 transitions with mass eigenstates which are not
CP eigenstates. A 1967 experiment [10] proved with
∆Le =
N (KL → π − e+ ν) − N (KL → π + e− ν)
= (2.24 ± 0.36) 10−3
N (KL → π − e+ ν) − N (KL → π + e− ν)
(1)
that CP symmetry is violated in K 0 K 0 transitions.
2
Phenomenology of K 0 K 0 Transitions
Following Weisskopf and Wigner [11], the evolution of the two-state neutral Kaon |Ψi =
ψ1 |K 0 i + ψ2 |K 0 i is given by the effective Schrödinger equation
i
∂
ψ1
ψ1
m11 m12
Γ11 Γ12
ψ1
i
= Hef f
=
−
. (2)
ψ2
m∗12 m22
ψ2
∂t ψ2
2 Γ∗12 Γ22
Owing to arbitrary phases of the states |K 0 i and |K 0 i, the phases of m12 and Γ12 are unobservable. Their difference, the phase of Γ12 /m12 , is an observable. In total, the equation has
7 real observable parameters: m11 , m22 , Γ11 , Γ22 , |m12 | and |Γ12 | in addition to φ(Γ12 /m12 ).
Two solutions of Eq. 2 have exponential decay laws,
√
KS0 (t) = [(1 + + δ) · K 0 + (1 − − δ) · K 0 ] · e−imS t−ΓS t/2 / 2 ,
√
KL0 (t) = [(1 + − δ) · K 0 − (1 − + δ) · K 0 ] · e−imL t−ΓL t/2 / 2 .
(3)
1
EUROPEAN ORGANISATION FOR NUCLEAR RESEARCH (CERN)
CERN-PH-EP-2014-157
arXiv:1411.1855v1 [hep-ex] 7 Nov 2014
Submitted to: Eur. Phys. J. C
Measurement of three-jet production cross-sections in pp
collisions at 7 TeV centre-of-mass energy using the ATLAS
detector
The ATLAS Collaboration
Abstract
Double-differential three-jet production cross-sections are measured in proton–proton collisions
√
at a centre-of-mass energy of s = 7 TeV using the ATLAS detector at the Large Hadron Collider.
The measurements are presented as a function of the three-jet mass (mjjj ), in bins of the sum of
the absolute rapidity separations between the three leading jets (|Y ∗ |). Invariant masses extending
up to 5 TeV are reached for 8 < |Y ∗ | < 10. These measurements use a sample of data recorded
using the ATLAS detector in 2011, which corresponds to an integrated luminosity of 4.51 fb−1 . Jets
are identified using the anti-kt algorithm with two different jet radius parameters, R = 0.4 and R =
0.6. The dominant uncertainty in these measurements comes from the jet energy scale. Next-toleading-order QCD calculations corrected to account for non-perturbative effects are compared to the
measurements. Good agreement is found between the data and the theoretical predictions based
on most of the available sets of parton distribution functions, over the full kinematic range, covering
almost seven orders of magnitude in the measured cross-section values.
c 2014 CERN for the benefit of the ATLAS Collaboration.
Reproduction of this article or parts of it is allowed as specified in the CC-BY-3.0 license.
BABAR-PUB-14/006
SLAC-PUB-15983
arXiv:1411.1842v1 [hep-ex] 7 Nov 2014
Study of CP asymmetry in B 0 -B 0 mixing with inclusive dilepton events
J. P. Lees,1 V. Poireau,1 V. Tisserand,1 E. Grauges,2 A. Palanoab ,3 G. Eigen,4 B. Stugu,4 D. N. Brown,5
L. T. Kerth,5 Yu. G. Kolomensky,5 M. J. Lee,5 G. Lynch,5 H. Koch,6 T. Schroeder,6 C. Hearty,7 T. S. Mattison,7
J. A. McKenna,7 R. Y. So,7 A. Khan,8 V. E. Blinovabc ,9 A. R. Buzykaeva ,9 V. P. Druzhininab ,9 V. B. Golubevab ,9
E. A. Kravchenkoab ,9 A. P. Onuchinabc ,9 S. I. Serednyakovab ,9 Yu. I. Skovpenab ,9 E. P. Solodovab ,9
K. Yu. Todyshevab ,9 A. J. Lankford,10 M. Mandelkern,10 B. Dey,11 J. W. Gary,11 O. Long,11 C. Campagnari,12
M. Franco Sevilla,12 T. M. Hong,12 D. Kovalskyi,12 J. D. Richman,12 C. A. West,12 A. M. Eisner,13
W. S. Lockman,13 W. Panduro Vazquez,13 B. A. Schumm,13 A. Seiden,13 D. S. Chao,14 C. H. Cheng,14
B. Echenard,14 K. T. Flood,14 D. G. Hitlin,14 T. S. Miyashita,14 P. Ongmongkolkul,14 F. C. Porter,14
M. Röhrken,14 R. Andreassen,15 Z. Huard,15 B. T. Meadows,15 B. G. Pushpawela,15 M. D. Sokoloff,15 L. Sun,15
P. C. Bloom,16 W. T. Ford,16 A. Gaz,16 J. G. Smith,16 S. R. Wagner,16 R. Ayad,17, a W. H. Toki,17 B. Spaan,18
D. Bernard,19 M. Verderi,19 S. Playfer,20 D. Bettonia ,21 C. Bozzia ,21 R. Calabreseab ,21 G. Cibinettoab ,21
E. Fioravantiab ,21 I. Garziaab ,21 E. Luppiab ,21 L. Piemontesea ,21 V. Santoroa ,21 A. Calcaterra,22 R. de Sangro,22
G. Finocchiaro,22 S. Martellotti,22 P. Patteri,22 I. M. Peruzzi,22, b M. Piccolo,22 M. Rama,22 A. Zallo,22
R. Contriab ,23 M. Lo Vetereab ,23 M. R. Mongeab ,23 S. Passaggioa ,23 C. Patrignaniab ,23 E. Robuttia ,23 B. Bhuyan,24
V. Prasad,24 A. Adametz,25 U. Uwer,25 H. M. Lacker,26 P. D. Dauncey,27 U. Mallik,28 C. Chen,29 J. Cochran,29
S. Prell,29 H. Ahmed,30 A. V. Gritsan,31 N. Arnaud,32 M. Davier,32 D. Derkach,32 G. Grosdidier,32
F. Le Diberder,32 A. M. Lutz,32 B. Malaescu,32, c P. Roudeau,32 A. Stocchi,32 G. Wormser,32 D. J. Lange,33
D. M. Wright,33 J. P. Coleman,34 J. R. Fry,34 E. Gabathuler,34 D. E. Hutchcroft,34 D. J. Payne,34
C. Touramanis,34 A. J. Bevan,35 F. Di Lodovico,35 R. Sacco,35 G. Cowan,36 J. Bougher,37 D. N. Brown,37
C. L. Davis,37 A. G. Denig,38 M. Fritsch,38 W. Gradl,38 K. Griessinger,38 A. Hafner,38 K. R. Schubert,38
R. J. Barlow,39, d G. D. Lafferty,39 R. Cenci,40 B. Hamilton,40 A. Jawahery,40 D. A. Roberts,40 R. Cowan,41
G. Sciolla,41 R. Cheaib,42 P. M. Patel,42, e S. H. Robertson,42 N. Neria ,43 F. Palomboab ,43 L. Cremaldi,44
R. Godang,44, f P. Sonnek,44 D. J. Summers,44 M. Simard,45 P. Taras,45 G. De Nardoab ,46 G. Onoratoab ,46
C. Sciaccaab ,46 M. Martinelli,47 G. Raven,47 C. P. Jessop,48 J. M. LoSecco,48 K. Honscheid,49 R. Kass,49
E. Feltresiab ,50 M. Margoniab ,50 M. Morandina ,50 M. Posoccoa ,50 M. Rotondoa ,50 G. Simiab ,50 F. Simonettoab ,50
R. Stroiliab ,50 S. Akar,51 E. Ben-Haim,51 M. Bomben,51 G. R. Bonneaud,51 H. Briand,51 G. Calderini,51
J. Chauveau,51 Ph. Leruste,51 G. Marchiori,51 J. Ocariz,51 M. Biasiniab ,52 E. Manonia ,52 S. Pacettiab ,52
A. Rossia ,52 C. Angeliniab ,53 G. Batignaniab ,53 S. Bettariniab ,53 M. Carpinelliab ,53, g G. Casarosaab ,53
A. Cervelliab ,53 M. Chrzaszcza ,53 F. Fortiab ,53 M. A. Giorgiab ,53 A. Lusianiac ,53 B. Oberhofab ,53 E. Paoloniab ,53
A. Pereza ,53 G. Rizzoab ,53 J. J. Walsha ,53 D. Lopes Pegna,54 J. Olsen,54 A. J. S. Smith,54 R. Facciniab ,55
F. Ferrarottoa ,55 F. Ferroniab ,55 M. Gasperoab ,55 L. Li Gioia ,55 A. Pilloniab ,55 G. Pireddaa ,55 C. B¨
unger,56
S. Dittrich,56 O. Gr¨
unberg,56 M. Hess,56 T. Leddig,56 C. Voß,56 R. Waldi,56 T. Adye,57 E. O. Olaiya,57
57
58
58
59, h
59
59
59
F. F. Wilson, S. Emery, G. Vasseur, F. Anulli,
D. Aston, D. J. Bard, C. Cartaro, M. R. Convery,59
J. Dorfan,59 G. P. Dubois-Felsmann,59 W. Dunwoodie,59 M. Ebert,59 R. C. Field,59 B. G. Fulsom,59
59
59
59
M. T. Graham, C. Hast, W. R. Innes, P. Kim,59 D. W. G. S. Leith,59 P. Lewis,59 D. Lindemann,59
S. Luitz,59 V. Luth,59 H. L. Lynch,59 D. B. MacFarlane,59 D. R. Muller,59 H. Neal,59 M. Perl,59, e T. Pulliam,59
B. N. Ratcliff,59 A. Roodman,59 A. A. Salnikov,59 R. H. Schindler,59 A. Snyder,59 D. Su,59 M. K. Sullivan,59
J. Va’vra,59 W. J. Wisniewski,59 H. W. Wulsin,59 M. V. Purohit,60 R. M. White,60, i J. R. Wilson,60
A. Randle-Conde,61 S. J. Sekula,61 M. Bellis,62 P. R. Burchat,62 E. M. T. Puccio,62 M. S. Alam,63 J. A. Ernst,63
R. Gorodeisky,64 N. Guttman,64 D. R. Peimer,64 A. Soffer,64 S. M. Spanier,65 J. L. Ritchie,66 A. M. Ruland,66
R. F. Schwitters,66 B. C. Wray,66 J. M. Izen,67 X. C. Lou,67 F. Bianchiab ,68 F. De Moriab ,68 A. Filippia ,68
D. Gambaab ,68 L. Lanceriab ,69 L. Vitaleab ,69 F. Martinez-Vidal,70 A. Oyanguren,70 P. Villanueva-Perez,70
J. Albert,71 Sw. Banerjee,71 A. Beaulieu,71 F. U. Bernlochner,71 H. H. F. Choi,71 G. J. King,71 R. Kowalewski,71
M. J. Lewczuk,71 T. Lueck,71 I. M. Nugent,71 J. M. Roney,71 R. J. Sobie,71 N. Tasneem,71 T. J. Gershon,72
P. F. Harrison,72 T. E. Latham,72 H. R. Band,73 S. Dasu,73 Y. Pan,73 R. Prepost,73 and S. L. Wu73
(The BABAR Collaboration)
1
Laboratoire d’Annecy-le-Vieux de Physique des Particules (LAPP),
3
57
Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom
58
CEA, Irfu, SPP, Centre de Saclay, F-91191 Gif-sur-Yvette, France
59
SLAC National Accelerator Laboratory, Stanford, California 94309 USA
60
University of South Carolina, Columbia, South Carolina 29208, USA
61
Southern Methodist University, Dallas, Texas 75275, USA
62
Stanford University, Stanford, California 94305-4060, USA
63
State University of New York, Albany, New York 12222, USA
64
Tel Aviv University, School of Physics and Astronomy, Tel Aviv, 69978, Israel
65
University of Tennessee, Knoxville, Tennessee 37996, USA
66
University of Texas at Austin, Austin, Texas 78712, USA
67
University of Texas at Dallas, Richardson, Texas 75083, USA
68
INFN Sezione di Torinoa ; Dipartimento di Fisica, Universit`
a di Torinob , I-10125 Torino, Italy
69
INFN Sezione di Triestea ; Dipartimento di Fisica, Universit`
a di Triesteb , I-34127 Trieste, Italy
70
IFIC, Universitat de Valencia-CSIC, E-46071 Valencia, Spain
71
University of Victoria, Victoria, British Columbia, Canada V8W 3P6
72
73
University of Wisconsin, Madison, Wisconsin 53706, USA
We present a measurement of the asymmetry ACP between same-sign inclusive dilepton samples
`+ `+ and `− `− (` = e, µ) from semileptonic B decays in Υ (4S) → BB events, using the complete
data set recorded by the BABAR experiment near the Υ (4S) resonance, corresponding to 471 million
BB pairs. The asymmetry ACP allows comparison between the mixing probabilities P(B 0 → B 0 )
and P(B 0 → B 0 ), and therefore probes CP and T violation. The result, ACP = (−3.9 ± 3.5(stat.) ±
1.9(syst.)) × 10−3 , is consistent with the Standard Model expectation.
PACS numbers: 13.20.He, 11.30.Er
A neutral B meson can transform to its antiparticle
through the weak interaction. A difference between the
probabilities P(B 0 → B 0 ) and P(B 0 → B 0 ) is allowed
by the Standard Model (SM), and is a signature of violations of both CP and T symmetries. This type of
CP violation, called CP violation in mixing, was first observed in the neutral kaon system [1], but has not been
observed in the neutral B system, where the SM predicts
an asymmetry of the order of 10−4 [2]. The current experimental average of CP asymmetry in mixing measured
in the B 0 system alone is ACP = (+2.3 ± 2.6) × 10−3 [3],
dominated by the BABAR [4, 5], DØ [6], and Belle [7]
experiments1 . A recent measurement in a mixture of B 0
and Bs0 mesons by the DØ collaboration deviates from
the SM expectation by more than three standard deviations [8]. Improving the experimental precision is crucial
for understanding the source of this apparent discrepancy.
The neutral B meson system can be described by an effective Hamiltonian H = M−iΓ/2 for the two states |B 0 i
and |B 0 i. Assuming CPT symmetry, the mass eigenstates
can be written as |BL/H i = p|B 0 i ± q|B 0 i. If |q/p| =
6 1,
both CP and T symmetries are violated. Details of the
formalism can be found in Refs. [10, 11].
The B 0 B 0 pair created in the Υ (4S) decay evolves
coherently until one B meson decays. In this analysis,
we use the charge of the lepton (electron or muon) in
1
The quoted average excludes the DØ inclusive dimuon result [8]
and the recently published LHCb result [9].
semileptonic B decays to identify the flavor of the B meson at the time of its decay. If the second B meson has
oscillated to its antiparticle, it will produce a lepton that
has the same charge as the lepton from the first B decay. The CP asymmetry ACP between P(B 0 → B 0 ) and
P(B 0 → B 0 ) can be measured by the charge asymmetry
±±
of the same-sign dilepton event rate P``
:
ACP =
++
−−
P``
− P``
1 − |q/p|4
.
++
−− =
1 + |q/p|4
P``
+ P``
(1)
This asymmetry is independent of the B decay time.
We present herein an updated measurement of ACP
using inclusive dilepton events collected by the BABAR
detector at the PEP-II asymmetric-energy e+ e− storage
rings at SLAC National Accelerator Laboratory. The
data set consists of 471 × 106 BB pairs produced at the
Υ (4S) resonance peak (on-peak) and 44 fb−1 of data collected at a center-of-mass (CM) energy 40 MeV below the
peak (off-peak) [12]. Monte Carlo (MC) simulated BB
events equivalent to 10 times the data set based on EvtGen [13] and GEANT4 [14] with full detector response
and event reconstruction are used to test the analysis
procedure. The main changes with respect to the previous BABAR analysis [4] include doubling the data set, a
higher signal selection efficiency, improved particle identification algorithms, and a time-independent approach
instead of a time-dependent analysis.
The BABAR detector is described in detail elsewhere [15]. Events are selected if the two highestmomentum particles in the event are consistent with the
electron or muon hypotheses. All quantities are evaluated
SLAC-PUB-16139
BABAR-PUB-14/008
arXiv:1411.1806v1 [hep-ex] 7 Nov 2014
Search for new π 0 -like particles produced in association with a τ -lepton pair
J. P. Lees,1 V. Poireau,1 V. Tisserand,1 E. Grauges,2 A. Palanoab ,3 G. Eigen,4 B. Stugu,4 D. N. Brown,5
L. T. Kerth,5 Yu. G. Kolomensky,5 M. J. Lee,5 G. Lynch,5 H. Koch,6 T. Schroeder,6 C. Hearty,7 T. S. Mattison,7
J. A. McKenna,7 R. Y. So,7 A. Khan,8 V. E. Blinovabc ,9 A. R. Buzykaeva ,9 V. P. Druzhininab ,9 V. B. Golubevab ,9
E. A. Kravchenkoab ,9 A. P. Onuchinabc ,9 S. I. Serednyakovab ,9 Yu. I. Skovpenab ,9 E. P. Solodovab ,9
K. Yu. Todyshevab ,9 A. J. Lankford,10 M. Mandelkern,10 B. Dey,11 J. W. Gary,11 O. Long,11 C. Campagnari,12
M. Franco Sevilla,12 T. M. Hong,12 D. Kovalskyi,12 J. D. Richman,12 C. A. West,12 A. M. Eisner,13
W. S. Lockman,13 W. Panduro Vazquez,13 B. A. Schumm,13 A. Seiden,13 D. S. Chao,14 C. H. Cheng,14
B. Echenard,14 K. T. Flood,14 D. G. Hitlin,14 T. S. Miyashita,14 P. Ongmongkolkul,14 F. C. Porter,14 M. Röhrken,14
R. Andreassen,15 Z. Huard,15 B. T. Meadows,15 B. G. Pushpawela,15 M. D. Sokoloff,15 L. Sun,15 P. C. Bloom,16
W. T. Ford,16 A. Gaz,16 J. G. Smith,16 S. R. Wagner,16 R. Ayad,17, a W. H. Toki,17 B. Spaan,18 D. Bernard,19
M. Verderi,19 S. Playfer,20 D. Bettonia ,21 C. Bozzia ,21 R. Calabreseab ,21 G. Cibinettoab ,21 E. Fioravantiab ,21
I. Garziaab ,21 E. Luppiab ,21 L. Piemontesea ,21 V. Santoroa ,21 A. Calcaterra,22 R. de Sangro,22 G. Finocchiaro,22
S. Martellotti,22 P. Patteri,22 I. M. Peruzzi,22, b M. Piccolo,22 M. Rama,22 A. Zallo,22 R. Contriab ,23
M. Lo Vetereab ,23 M. R. Mongeab ,23 S. Passaggioa ,23 C. Patrignaniab ,23 E. Robuttia ,23 B. Bhuyan,24 V. Prasad,24
A. Adametz,25 U. Uwer,25 H. M. Lacker,26 U. Mallik,27 C. Chen,28 J. Cochran,28 S. Prell,28 H. Ahmed,29
A. V. Gritsan,30 N. Arnaud,31 M. Davier,31 D. Derkach,31 G. Grosdidier,31 F. Le Diberder,31 A. M. Lutz,31
B. Malaescu,31, c P. Roudeau,31 A. Stocchi,31 G. Wormser,31 D. J. Lange,32 D. M. Wright,32 J. P. Coleman,33
J. R. Fry,33 E. Gabathuler,33 D. E. Hutchcroft,33 D. J. Payne,33 C. Touramanis,33 A. J. Bevan,34 F. Di Lodovico,34
R. Sacco,34 G. Cowan,35 J. Bougher,36 D. N. Brown,36 C. L. Davis,36 A. G. Denig,37 M. Fritsch,37 W. Gradl,37
K. Griessinger,37 A. Hafner,37 K. R. Schubert,37 R. J. Barlow,38, d G. D. Lafferty,38 R. Cenci,39 B. Hamilton,39
A. Jawahery,39 D. A. Roberts,39 R. Cowan,40 G. Sciolla,40 R. Cheaib,41 P. M. Patel,41, e S. H. Robertson,41
N. Neria ,42 F. Palomboab ,42 L. Cremaldi,43 R. Godang,43, f P. Sonnek,43 D. J. Summers,43 M. Simard,44 P. Taras,44
G. De Nardoab ,45 G. Onoratoab ,45 C. Sciaccaab ,45 M. Martinelli,46 G. Raven,46 C. P. Jessop,47 J. M. LoSecco,47
K. Honscheid,48 R. Kass,48 E. Feltresiab ,49 M. Margoniab ,49 M. Morandina ,49 M. Posoccoa ,49 M. Rotondoa ,49
G. Simiab ,49 F. Simonettoab ,49 R. Stroiliab ,49 S. Akar,50 E. Ben-Haim,50 M. Bomben,50 G. R. Bonneaud,50
H. Briand,50 G. Calderini,50 J. Chauveau,50 Ph. Leruste,50 G. Marchiori,50 J. Ocariz,50 M. Biasiniab ,51
E. Manonia ,51 S. Pacettiab ,51 A. Rossia ,51 C. Angeliniab ,52 G. Batignaniab ,52 S. Bettariniab ,52 M. Carpinelliab ,52, g
G. Casarosaab ,52 A. Cervelliab ,52 M. Chrzaszcza ,52 F. Fortiab ,52 M. A. Giorgiab ,52 A. Lusianiac ,52 B. Oberhofab ,52
E. Paoloniab ,52 A. Pereza ,52 G. Rizzoab ,52 J. J. Walsha ,52 D. Lopes Pegna,53 J. Olsen,53 A. J. S. Smith,53
R. Facciniab ,54 F. Ferrarottoa ,54 F. Ferroniab ,54 M. Gasperoab ,54 L. Li Gioia ,54 A. Pilloniab ,54 G. Pireddaa ,54
C. B¨
unger,55 S. Dittrich,55 O. Gr¨
unberg,55 M. Hess,55 T. Leddig,55 C. Voß,55 R. Waldi,55 T. Adye,56 E. O. Olaiya,56
F. F. Wilson,56 S. Emery,57 G. Vasseur,57 F. Anulli,58, h D. Aston,58 D. J. Bard,58 C. Cartaro,58 M. R. Convery,58
J. Dorfan,58 G. P. Dubois-Felsmann,58 W. Dunwoodie,58 M. Ebert,58 R. C. Field,58 B. G. Fulsom,58
M. T. Graham,58 C. Hast,58 W. R. Innes,58 P. Kim,58 D. W. G. S. Leith,58 P. Lewis,58 D. Lindemann,58 S. Luitz,58
V. Luth,58 H. L. Lynch,58 D. B. MacFarlane,58 D. R. Muller,58 H. Neal,58 M. Perl,58, e T. Pulliam,58 B. N. Ratcliff,58
A. Roodman,58 A. A. Salnikov,58 R. H. Schindler,58 A. Snyder,58 D. Su,58 M. K. Sullivan,58 J. Va’vra,58
W. J. Wisniewski,58 H. W. Wulsin,58 M. V. Purohit,59 R. M. White,59, i J. R. Wilson,59 A. Randle-Conde,60
S. J. Sekula,60 M. Bellis,61 P. R. Burchat,61 E. M. T. Puccio,61 M. S. Alam,62 J. A. Ernst,62 R. Gorodeisky,63
N. Guttman,63 D. R. Peimer,63 A. Soffer,63 S. M. Spanier,64 J. L. Ritchie,65 R. F. Schwitters,65 B. C. Wray,65
J. M. Izen,66 X. C. Lou,66 F. Bianchiab ,67 F. De Moriab ,67 A. Filippia ,67 D. Gambaab ,67 L. Lanceriab ,68 L. Vitaleab ,68
F. Martinez-Vidal,69 A. Oyanguren,69 P. Villanueva-Perez,69 J. Albert,70 Sw. Banerjee,70 A. Beaulieu,70
F. U. Bernlochner,70 H. H. F. Choi,70 G. J. King,70 R. Kowalewski,70 M. J. Lewczuk,70 T. Lueck,70
D. McKeen,70, j I. M. Nugent,70 M. Pospelov,70, k J. M. Roney,70 R. J. Sobie,70 N. Tasneem,70 T. J. Gershon,71
P. F. Harrison,71 T. E. Latham,71 H. R. Band,72 S. Dasu,72 Y. Pan,72 R. Prepost,72 and S. L. Wu72
(The BABAR Collaboration)
1
Laboratoire d’Annecy-le-Vieux de Physique des Particules (LAPP),
Université de Savoie, CNRS/IN2P3, F-74941 Annecy-Le-Vieux, France
Universitat de Barcelona, Facultat de Fisica, Departament ECM, E-08028 Barcelona, Spain
3
INFN Sezione di Baria ; Dipartimento di Fisica, Universit`
a di Barib , I-70126 Bari, Italy
4
University of Bergen, Institute of Physics, N-5007 Bergen, Norway
5
Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720, USA
6
Ruhr Universit¨
at Bochum, Institut f¨
ur Experimentalphysik 1, D-44780 Bochum, Germany
2
3
63
Tel Aviv University, School of Physics and Astronomy, Tel Aviv, 69978, Israel
64
University of Tennessee, Knoxville, Tennessee 37996, USA
65
University of Texas at Austin, Austin, Texas 78712, USA
66
University of Texas at Dallas, Richardson, Texas 75083, USA
67
INFN Sezione di Torinoa ; Dipartimento di Fisica, Universit`
a di Torinob , I-10125 Torino, Italy
68
INFN Sezione di Triestea ; Dipartimento di Fisica, Universit`
a di Triesteb , I-34127 Trieste, Italy
69
IFIC, Universitat de Valencia-CSIC, E-46071 Valencia, Spain
70
University of Victoria, Victoria, British Columbia, Canada V8W 3P6
71
72
University of Wisconsin, Madison, Wisconsin 53706, USA
We report on a search in e+ e− annihilations for new π 0 -like particles produced in association
with a τ -lepton pair. These objects, with a similar mass and similar decay modes to π 0 mesons,
could provide an explanation for the non-asymptotic behavior of the pion-photon transition form
factor observed by the BABAR Collaboration. No significant signal is observed, and limits on the
production cross section at the level of 73 fb or 370 fb, depending on the model parameters, are
determined at 90% confidence level. These upper limits lie below the cross section values needed to
explain the BABAR form factor data.
PACS numbers: 14.40.Rt, 14.60.Fg
I.
INTRODUCTION
The measurement
of the pion-photon transition form
factor Fπ0 Q2 reported by the BABAR Collaboration [1]
has given rise to much discussion [2–5]. The result does
not exhibit convergence towards the Brodsky-Lepage
limit of 185 MeV/Q2 [6] even for large values of the
squared momentum transfer, viz., Q2 > 15 GeV, where
the data are expected to be well described by perturbative QCD. Results from the Belle Collaboration [7] show
better agreement with the perturbative predictions but
are consistent with the BABAR data within the uncertainties.
A recent suggestion [8] proposes that the observed lack
of asymptotic behavior might be due to the production of
new particles or states, tentatively named “pion impostors” and generically denoted φ [9]. Two classes of models
are considered. In the first, scalar φS or pseudoscalar φP
particles are introduced with a mass within 10 MeV/c2 of
0
the π 0 mass, and with similar decay modes to the
π ,
such that they thereby contribute to the Fπ0 Q2 measurement. In the second, a new light pseudoscalar state
a
b
c
d
e
f
g
h
i
j
k
Now at: University of Tabuk, Tabuk 71491, Saudi Arabia
Also at: Universit`
a di Perugia, Dipartimento di Fisica, I-06123
Perugia, Italy
Now at: Laboratoire de Physique Nucl´
eaire et de Hautes Energies, IN2P3/CNRS, F-75252 Paris, France
Now at: University of Huddersfield, Huddersfield HD1 3DH, UK
Deceased
Now at: University of South Alabama, Mobile, Alabama 36688,
USA
Also at: Universit`
a di Sassari, I-07100 Sassari, Italy
Also at: INFN Sezione di Roma, I-00185 Roma, Italy
Now at: Universidad T´
ecnica Federico Santa Maria, 2390123
Valparaiso, Chile
Now at: University of Washington, Seattle, Washington 98195,
USA
Also at: Perimeter Institute for Theoretical Physics, Waterloo,
Ontario, Canada N2J 2W9
mixes with the π 0 to produce a so-called “hardcore pion”
0
0
πHC
. The φP and πHC
have similar experimental signatures and the related processes only differ in their production rates. These models predict large coupling strengths
between the new objects and the τ lepton, comparable to
the strength of the strong force, leading to an observable
increase of Fπ0 Q2 through virtual loops with τ leptons.
The couplings of the new particles to heavy quarks and
other Standard Model (SM) particles are constrained by
experimental data to be an order of magnitude or more
smaller [8].
The largeness of the predicted couplings of the pion
impostors to the τ lepton, and the absence of corresponding experimental constraints, motivate a search for pion
impostors radiated from τ leptons in e+ e− → τ + τ − φ,
φ → γγ interactions. This process is particularly compelling because the rate of such events must
be considerable in order to explain the BABAR Fπ0 Q2 data, making
it potentially observable. The production cross sections
required to describe the BABAR measurements are listed
in Table I. The corresponding results for the combined
BABAR and Belle data are also given. Based on the cross
sections derived from the BABAR data alone, on the order
of 105 events are expected in the BABAR data sample.
0
TABLE I. Production cross sections
of e+ e− → τ + τ − πHC
,
√
τ + τ − φP , and τ + τ − φS at s = 10.58 GeV needed to accommodate the pion-photon transition form factor reported
by BABAR, as well as the combination of BABAR and Belle
measurements. Confidence intervals at 95% confidence level
are provided in brackets.
Model
0
πHC
φP
φS
σ(pb)
BABAR [1]
0.62
4.8
130
[0.25 – 0.84]
[2.5 – 6.9]
[70 – 180]
σ(pb)
BABAR + Belle [7]
0.44
3.4
90
[0.15 – 0.59]
[ 2.5 – 5.1]
[ 50 – 140]
Statistics of thermalization in Bjorken Flow
´ ski‡2,3
Jakub Jankowski∗1 , Grzegorz Plewa†2 , and Michal Spalin
arXiv:1411.1969v1 [hep-th] 7 Nov 2014
1 Institute
of Physics, Jagiellonian University, ul. Lojasiewicza 11, 30-348 Krak´
ow, Poland
2 National
3 Physics
Center for Nuclear Research, ul. Ho˙za 69, 00-681 Warsaw, Poland
Department, University of Bialystok, ul. Lipowa 41, 15-424 Bialystok, Poland
Abstract
The apparent early thermalization of quark-gluon plasma produced at RHIC and
LHC has motivated a number of studies of strongly coupled N = 4 supersymmetric
Yang-Mills theory using the AdS/CFT correspondence. Here we present the results
of numerical simulations of Bjorken flow aimed at establishing typical features of the
dynamics. This is done by evolving a large number of far from equilibrium initial
states well into the hydrodynamic regime. The results strongly suggest that early
thermalization is generic in this theory, taking place at proper times around 0.6 in
units of inverse local temperature. We also find that the scale which determines the
rate of hydrodynamic cooling is linearly correlated with the entropy of initial states
defined by the area of the apparent horizon in the dual geometry. Our results also
suggest that entropy production during the hydrodynamic stage of evolution is not
negligible despite the low value of η/s.
∗
Email: [email protected]
‡
†
Heavy-Meson Spectrum Tests of the Oktay–Kronfeld
Action
arXiv:1411.1823v1 [hep-lat] 7 Nov 2014
Jon A. Bailey, Yong-Chull Jang∗, Weonjong Lee
Lattice Gauge Theory Research Center, CTP, and FPRD,
Department of Physics and Astronomy, Seoul National University, Seoul, 151-747, South Korea
Carleton DeTar
Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA
Andreas S. Kronfeld
Theoretical Physics Department, Fermilab, Batavia, IL 60510, USA
Institute for Advanced Study, Technische Universität München, 85748 Garching, Germany
Mehmet B. Oktay
Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA
Fermilab Lattice, MILC, and SWME Collaborations
We present heavy-meson spectrum results obtained using the Oktay–Kronfeld (OK) action on
MILC asqtad lattices. The OK action was designed to improve the heavy-quark action of the
Fermilab formulation, such that heavy-quark discretization errors are reduced. The OK action
includes dimension-6 and -7 operators necessary for tree-level matching to QCD through order
O(Λ3 /m3Q ) for heavy-light mesons and O(v6 ) for quarkonium, or, equivalently, through O(a2 )
with some O(a3 ) terms with Symanzik power counting. To assess the improvement, we extend
previous numerical tests with heavy-meson masses by analyzing data generated on a finer (a ≈
0.12 fm) lattice with the correct tadpole factors for the c5 term in the action. We update the
analyses of the inconsistency parameter and the hyperfine splittings for the rest and kinetic masses.
The 32nd International Symposium on Lattice Field Theory
23-28 June, 2014
Columbia University, New York, NY
∗ Speaker.
c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
http://pos.sissa.it/
Yong-Chull Jang
Heavy-Meson Spectrum Tests of the OK Action
1. Introduction
The parameter εK quantifies indirect CP violation in the neutral kaon system. At present, the
tension between the Standard Model (SM) and experimental values of |εK | is 3.4σ [1] with the
value of |Vcb | from the exclusive decay B → D∗ `ν [2]. This value of |Vcb |, the most precise from
exclusive decays to date, is 3σ away from the value from inclusive decays [3]. The largest error
in the εK determination in the SM comes from |Vcb |, so it is crucial to improve the precision of
exclusive
The dominant error of exclusive |Vcb | comes from the heavy-quark discretization error in the
form-factor calculation of the semi-leptonic decay B → D∗ `ν [2]. Hence, the SWME Collaboration
plans to use the Oktay–Kronfeld (OK) action [4] in the upcoming calculation in order to reduce
it efficiently. This action is an improved version of the Fermilab action [5], which incorporates
the dimension-6 and -7 bilinear operators needed for tree-level matching to QCD through order
O(Λ3 /m3Q ) for heavy-light mesons and O(v6 ) for quarkonium. We expect that the bottom- and
charm-quark discretization errors could be reduced below the current 1% level. A similar error for
the charm-quark could also be achieved with other highly-improved actions, such as HISQ [6].
For the heavy-meson spectrum, we present results for the inconsistency parameter [7, 8] and
hyperfine splittings, all of which test how well the Fermilab and OK actions perform in practice.
For this purpose, we follow the strategy of our previous work [9], in which the c5 term was not
completely tadpole-improved. In this work, we now implement the tadpole improvement for c5
completely. We also extend the data analysis to data sets produced on a finer (a ≈ 0.12 fm) MILC
asqtad lattice.
2. Meson Correlators
We use a subset of the MILC N f = 2 + 1 asqtad ensembles at a = 0.12 fm and 0.15 fm [11],
summarized in Table 1. We compute meson correlators C(t, p )
C(t, p ) = ∑ eipp·xx hO † (t, x )O(0, 0 )i .
(2.1)
x
The interpolating operators O(x) are
Ot (x) = ψ¯ α (x)Γαβ Ωβ t (x)χ(x)
O(x) = ψ¯ α (x)Γαβ ψβ (x)
(heavy-light meson) ,
(2.2)
(quarkonium) ,
(2.3)
where the heavy-quark field ψ is that of the OK action, while the light-quark field χ is that of the
asqtad action. The spin structure is Γ = γ5 for the pseudoscalar and Γ = γi for the vector meson.
a(fm) NL3 × NT
aml
ams
0.12 203 × 64 6.79 0.02
0.05
β
u0
a−1 (GeV) Nconf Ntsrc
0.8688 1.683+43
−16
484
6
0.15 163 × 48 6.60 0.029 0.0484 0.8614 1.350+35
−13
500
4
Table 1: Parameters of the MILC asqtad ensembles with N f = 2 + 1 flavors [10].
2
Mon. Not. R. Astron. Soc. 000, 000–000 (0000)
Printed 10 November 2014
(MN LATEX style file v2.2)
Reply to Two Comments on “Dark matter searches going bananas
the contribution of Potassium (and Chlorine) to the 3.5 keV line”
Tesla
Jeltema1? and Stefano Profumo1 †
1
arXiv:1411.1759v1 [astro-ph.HE] 6 Nov 2014
Department of Physics and Santa Cruz Institute for Particle Physics University of California, Santa Cruz, CA 95064, USA
10 November 2014
ABSTRACT
We respond to two comments on our recent paper, Jeltema & Profumo (2014). The first comment by Boyarsky et al. confirms the absence of a line from M31 in the 3-4 keV energy
range, but criticizes the choice of that energy range for spectral fitting on the basis that (i)
the background model adopted between 3-4 keV is invalid outside that range and that (ii)
extending the energy range multiple features appear, including a 3.5 keV line. Point (i) is
manifestly irrelevant (the 3-4 keV background model was not meant to extend outside that
range), while closer inspection of point (ii) shows that the detected features are inconsistent
and likely unphysical. We demonstrate that the existence of an excess near 3.5 keV in the M31
data requires fitting a broad enough energy range such that the background modeling near 3.5
keV is poor to a level that multiple spurious residual features become significant. Bulbul et
al. criticize our use of WebGuide instead of the full AtomDB package. While a technically
correct remark, this is only a red herring: our predictions are based on line ratios, and not on
absolute emissivities; line ratios, for atomic transitions with similar peak temperatures, are
largely temperature-independent, therefore the line ratios we employed to draw our conclusions are substantially correct. Bulbul et al. also present a new analysis of their data at lower
energy, which excludes a significant Cl contamination to the 3.5 keV line. This is a welcome
new element, but irrelevant to our main criticism of their analysis, since Cl XVII emission was
predicted to be subdominant to K XVIII. Both of the Bulbul et al.’s criticisms are thus entirely
inconsequential to the conclusions we drew in our original study. Finally, we demonstrate
that the multi-temperature models employed in Bulbul et al. are, in fact, inconsistent, based
on the Ca XX to Ca XIX line ratio, which is a solid test, independent of relative elemental
abundances; we show that the overestimated cluster plasma temperatures they employ lead to
gross underestimates of the K XVIII line emissivity.
Key words: dark matter – line: identification – Galaxy: centre – X-rays: galaxies – X-rays:
galaxies: clusters
1
INTRODUCTION
In 2009, one of the co-authors of Bulbul et al. (2014a) reported the
discovery of an unidentified 2.5 keV line from the supposed ultrafaint dwarf spheroidal galaxy Willman 1 with Chandra (Loewenstein & Kusenko 2010). Excitement and model building efforts ensued, motivated by the possibility that this line originated from
the radiative decay of 5 keV sterile neutrinos into an active neutrino and a photon; the fact that the resulting sterile neutrino particle properties would potentially also explain pulsar kicks was, in
the words of the authors, additionally “bolstering both the statistical and physical significance of [the] measurement”. Boyarsky and
collaborators subsequently questioned the sterile neutrino interpretation of the 2.5 keV signal, based, notably, on the non-detection of
?
[email protected]
† [email protected]
c 0000 RAS
any lines from M31, and outlined a vade mecum on how to “check
the dark matter origin of a spectral feature” (Boyarsky et al. 2010).
Kusenko & Loewenstein (2010) then promptly proceeded to criticize Boyarsky et al’s findings, principally based on the dark matter
density profile choice for M31. Eventually, new XMM observations (Loewenstein & Kusenko 2012) conclusively showed that no
statistically significant line existed from Willman 1.
Earlier this year, Bulbul et al. (2014a) reported the detection
of an unidentified X-ray line at an energy of about 3.5 keV from
various observations and different sub-samples of stacked clusters
of galaxies, and entertained the possibility that the unidentified line
originated from sterile neutrino decays, short of any plausible, more
mundane astrophysical explanation. Shortly thereafter, Boyarsky
et al. (2014a) confirmed the existence of a 3.5 keV line from the
Perseus cluster and, interestingly, from M31. Concurrently with
significant model building work, other investigators scrutinized Xray data to further seek confirmation for, and/or to constrain, the 3.5
arXiv:1411.1758v1 [astro-ph.HE] 6 Nov 2014
Prepared for submission to JCAP
Where do the 3.5 keV photons come
from? A morphological study of the
Galactic Center and of Perseus
Eric Carlson,a,b Tesla Jeltema,a,b Stefano Profumoa,b
a Department
of Physics, University of California, Santa Cruz
1156 High St, Santa Cruz, CA 95064
b Santa Cruz Institute for Particle Physics,
1156 High St, Santa Cruz, CA 95064
E-mail: [email protected], [email protected], [email protected]
Abstract. We test the origin of the 3.5 keV line photons by analyzing the morphology
of the emission at that energy from the Galactic Center and from the Perseus cluster of
galaxies. We employ a variety of different templates to model the continuum emission
and analyze the resulting radial and azimuthal distribution of the residual emission. We
then perform a pixel-by-pixel binned likelihood analysis including line emission templates and dark matter templates and assess the correlation of the 3.5 keV emission
with these templates. We conclude that the radial and azimuthal distribution of the
residual emission is incompatible with a dark matter origin for both the Galactic center
and Perseus; the Galactic center 3.5 keV line photons trace the morphology of lines at
comparable energy, while the Perseus 3.5 keV photons are highly correlated with the
cluster’s cool core, and exhibit a morphology incompatible with either dark matter decay or with axion-like particle conversions in the cluster’s magnetic fields. The template
analysis additionally allows us to set the most stringent constraints to date on lines in
the 3.5 keV range from dark matter decay.
TU-985, IPMU14-0334
Resonant conversions of QCD axions into hidden axions and
suppressed isocurvature perturbations
arXiv:1411.2011v1 [hep-ph] 7 Nov 2014
Naoya Kitajima a∗ , Fuminobu Takahashi a,b†
a
b
Department of Physics, Tohoku University, Sendai 980-8578, Japan
Kavli IPMU, TODIAS, University of Tokyo, Kashiwa 277-8583, Japan
Abstract
We study in detail MSW-like resonant conversions of QCD axions into hidden axions, including
cases where the adiabaticity condition is only marginally satisfied, and where anharmonic effects
are non-negligible. When the resonant conversion is efficient, the QCD axion abundance is
suppressed by the hidden and QCD axion mass ratio. We find that, when the resonant conversion
is incomplete due to a weak violation of the adiabaticity, the CDM isocurvature perturbations can
be significantly suppressed, while non-Gaussianity of the isocurvature perturbations generically
remain unsuppressed. The isocurvature bounds on the inflation scale can therefore be relaxed
by the partial resonant conversion of the QCD axions into hidden axions.
∗
†
email: [email protected]
email: [email protected]
1
JLAB-THY-14-1982
DAMTP-2014-81
Resonances in coupled πK, ηK scattering from lattice QCD
David J. Wilson,1 Jozef J. Dudek,2, 1, ∗ Robert G. Edwards,2 and Christopher E. Thomas3
(for the Hadron Spectrum Collaboration)
1
Department of Physics, Old Dominion University, Norfolk, VA 23529, USA
Theory Center, Jefferson Lab, 12000 Jefferson Avenue, Newport News, VA 23606, USA
3
Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences,
University of Cambridge, Wilberforce Road, Cambridge, CB3 0WA, UK
arXiv:1411.2004v1 [hep-ph] 7 Nov 2014
2
Coupled-channel πK and ηK scattering amplitudes are determined by studying the finite-volume
energy spectra obtained from dynamical lattice QCD calculations. Using a large basis of interpolating operators, including both those resembling a q q¯ construction and those resembling a pair of
mesons with relative momentum, a reliable excited-state spectrum can be obtained. Working at
mπ = 391 MeV, we find a gradual increase in the J P = 0+ πK phase-shift which may be identified
with a broad scalar resonance that couples strongly to πK and weakly to ηK. The low-energy
behavior of this amplitude suggests a virtual bound-state that may be related to the κ resonance.
A bound state with J P = 1− is found very close to the πK threshold energy, whose coupling to the
πK channel is compatible with that of the experimental K ? (892). Evidence is found for a narrow
resonance in J P = 2+ . Isospin–3/2 πK scattering is also studied and non-resonant phase-shifts
spanning the whole elastic scattering region are obtained.
I.
INTRODUCTION
Understanding the spectrum and properties of excited
hadron states directly from the underlying theory of
quarks and gluons, Quantum Chromodynamics (QCD),
remains an unsolved problem. One challenge lies in the
fact that excited hadrons are not asymptotically observable states, but rather appear as resonant enhancements
in the scattering of lighter stable hadrons. Another challenge is the difficulty of computation within QCD which,
at the energy scales of relevance, is a non-perturbative,
relativistic theory. One technique which has shown significant progress when applied to hadron spectroscopy is
lattice QCD. Lattice QCD is a systematically improvable
calculational scheme in which the quark and gluon fields
are discretized on a finite cubic grid, rendering the theory
amenable to numerical computation. Monte-Carlo sampling of possible field configurations leads to estimates
for hadronic correlation functions whose spectral content
can then be explored.
The interactions of the lightest octet of pseudoscalar
mesons are important since they are the stable particles
to which excited hadrons decay. In this manuscript we
will explore πK scattering using lattice QCD techniques.
This channel, having net strangeness, cannot proceed
through intermediate quarkless states, which simplifies
the phenomenology with respect to isospin–0 channels in
which glueball states may appear.
The bulk of our knowledge of kaon scattering amplitudes comes from kaon beam experiments at SLAC in the
1970s and 80s. πK scattering amplitudes were extracted
from reactions using a proton target by extrapolating
to small momentum transfer, t, where nearly-on-shell
∗
[email protected]
pion exchange dominates. Phase-shift analysis of the
flavor exotic isospin–3/2 amplitudes as extracted from
K + p → K + π + n and K − p → K − π − ∆++ by Estabrooks
et al [1] indicates a weak repulsive interaction in S-wave
and very weak interactions in P -wave and higher.
In isospin–1/2, as well as the phase-shift analysis of
Estabrooks et al, there is a considerable set of πK scattering results provided by the LASS experiment – of particular relevance here are the final states πK [2], ηK [3]
and ππK [4]. In the partial-wave analysis of πK → πK,
a peaking amplitude in S-wave is interpreted as a broad
K0? (1430) resonance which appears to saturate unitarity.
The narrow elastic vector resonance, K ? (892), presents
itself as a rapid rise in the P -wave phase-shift. The Dwave amplitude has a peak, well below the unitarity limit,
that can be interpreted as an inelastic K2? (1430) resonance. Further resonances in the “natural parity” series
(J P = 3− , 4+ , 5− ) are observed at higher energies.
ηK is the first inelastic channel to open, but LASS
reports no significant amplitude into ηK for Ecm < 2 GeV
in S, P and D waves. Indeed the inelasticity in P, Dwaves and higher appears to come first from the ππK
final state, where a significant amplitude is seen in 1−
above 1.3 GeV and a peak in 2+ at the K2? (1430). ππK
also couples to the “unnatural parity” series, notably to
J P = 1+ , where peaking behavior is observed that is
commonly described in terms of two axial resonances,
K1 (1270), K1 (1400).
Resonances may or may not appear as bumps in
hadron scattering amplitudes, and the least modeldependent way to describe them is as pole singularities
in the analytic continuation of a scattering amplitude
to complex values of energy. Narrow resonances, corresponding to sharp peaks in amplitudes, or rapid phase
motion, appear as poles that lie close to the real energy
axis where scattering amplitudes are determined experimentally. Poles that lie further away can lead to less
CYCU-HEP-14-07
Correlating New Physics in Bq0 → µ+ µ− , φs , and K → πν ν
¯ Decays
a
Wei-Shu Houa , Masaya Kohdaa,b , and Fanrong Xua,c
arXiv:1411.1988v1 [hep-ph] 7 Nov 2014
Department of Physics, National Taiwan University, Taipei, Taiwan 10617
b
Department of Physics, Chung-Yuan Christian University, Chung-Li, Taiwan 32023
c
Department of Physics, Liaoning Normal University, Dalian 116029, P.R. China
The long-awaited Bs → µ+ µ− mode has finally been observed at rate consistent with Standard
Model, albeit lower by 1.2σ. There is some hint for New Physics in the rarer Bd0 → µ+ µ− decay,
especially if the currently 2.2σ-enhanced central value persists with more data. The measurement
¯ and J/ψππ modes, has reached Standard Model
of CP violating phase φs , via both Bs → J/ψK K
sensitivity. These measurements stand major improvement when LHC enters Run 2. Concurrently,
the KL → π 0 ν ν¯ and K + → π + ν ν¯ modes are being pursued in a similar time frame. We illustrate the
possible correlations between New Physics effects in these four modes, using the fourth generation as
example. While correlations may or may not exist in other New Physics models, the four generation
model can accommodate enhancements in both Bd0 → µ+ µ− and KL → π 0 ν ν¯.
PACS numbers: 14.65.Jk 12.15.Hh 11.30.Er 13.20.He
I.
INTRODUCTION
The 7-and-8 TeV run (Run 1) of the LHC has brought
about much progress in particle physics, even though
no New Physics (NP) has been uncovered. The hint
of possible NP in the forward-backward asymmetry of
B → K ∗ ℓ+ ℓ− decay [1] from the B factories was eliminated by the measurement of B 0 → K ∗0 µ+ µ− by LHCb
with just 0.37 fb−1 data [2]. Although with much anticipation, the possibility or hint of large CP violating
0
(CPV) phase φs in Bs0 –B s meson mixing at the Tevatron [3, 4] was also eliminated by the combined measurements of the Bs0 → J/ψ φ [5] and Bs0 → J/ψ f0 (980) [6]
channels, with 0.37 fb−1 and 0.41 fb−1 data, respectively.
Thus, the thread that started with the suggested possible
correlations [7] with large direct CPV difference ∆AKπ ≡
A(B + → K + π 0 ) − A(B 0 → K + π − ) [8], if the source for
the latter arises from the electroweak penguin [9], was
vanquished. Finally, the hot pursuit for Bs0 → µ+ µ−
at the Tevatron was overtaken by the LHC, culminating in the observation by the LHCb [10] and CMS [11]
experiments [12], albeit again consistent with the Standard Model (SM). This deals another blow to minimal
supersymmetric SM (MSSM), where the Bs0 → µ+ µ−
rate could have been enhanced by three orders of magnitude, the original reason behind the frenzied pursuit!
However, LHC Run 1 has brought on its own tantalizing hints. The full combination results of CMS and
LHCb for Bs0 → µ+ µ− and the even rarer Bd0 → µ+ µ−
decay have been announced recently [13],
−9
B(Bs0 → µ+ µ− ) = (2.8+0.7
,
−0.6 ) × 10
B(Bd0
+ −
→µ µ )=
(3.9+1.6
−1.4 )
× 10
−10
(1)
.
(2)
At 6.2σ significance, the Bs0 → µ+ µ− mode is genuinely
observed. The SM expected value, however, would have
given 7.6σ, hence a mild “suppression” is suggested. On
the other hand, the Bd0 → µ+ µ− mode, nonzero at the
3.2σ level, is consistent with SM expectation of (1.06 ±
0.09) × 10−10 [14] only at 2.2σ level. While 2.2σ should
not be taken seriously as a deviation, but if the current
central value persists with much more data, it would be
more than 3 times enhanced compared with SM! Thus,
Bd0 → µ+ µ− is the mode to watch at the up and coming
LHC Run 2 (13 and 14 TeV).
Compared with initial 7 TeV data, the 1 fb−1 LHCb
update for φs [15] is also providing new implications:
φs = 0.01 ± 0.07 ± 0.01,
(1 fb
−1
, LHCb)
(3)
which combines both the Bs0 → J/ψ φ and J/ψ π + π −
channels, with respective values
−1
¯ LHCb) (4)
J/ψK K,
−1
J/ψ ππ, LHCb)
φs = 0.07 ± 0.09 ± 0.01, (1 fb
φs = −0.14+0.17
−0.16 ± 0.01, (1 fb
(5)
which are of opposite sign. Eq. (5) is improved from
an earlier [16] 1 fb−1 result of −0.019+0.173+0.004
−0.174−0.003 , mainly
due to improvements in tagging of the Bs0 flavor, i.e. particle or anti-particle. With same tagging, Eq. (4) is improved from the 0.37 fb−1 result of 0.15 ± 0.18 ± 0.06.
Eq. (3) dominates the Heavy Flavor Averaging Group
(HFAG) combination [17] of all experiments,
φs = 0.00 ± 0.07,
(PDG2014)
(6)
which is adopted by the Particle Data Group (PDG) [18].
The PDG 2014 result, Eq. (6), may seem to imply
that it would take a long while to probe New Physics via
deviations from the SM expectation of φs ≃ −0.04. This
is especially so since the preliminary result [19] of CMS
based on 20 fb−1 data,
φs = −0.03 ± 0.11 ± 0.03, (20 fb−1 , CMS)
(7)
which is mildly negative, is not included in the PDG 2014
combination. However, with 3 fb−1 data at hand, LHCb
has already updated its result in the Bs0 → J/ψ π + π −
mode to full Run 1 data [20]:
−1
φs = 0.070 ± 0.068 ± 0.008. (3 fb
J/ψ ππ, LHCb) (8)
arXiv:1411.1983v1 [hep-ph] 7 Nov 2014
A Monte Carlo study of jet fragmentation functions in PbPb and pp collisions
√
at s = 2.76 TeV
Redamy Pérez-Ramos1
2 3 4 5,
Thorsten Renk 6 7
8
The parton-to-hadron fragmentation functions (FFs) obtained from the YAJEM and PYTHIA6 Monte Carlo
event generators, are studied for jets produced in a strongly-interacting medium and in the QCD “vacuum”
respectively. The medium modifications are studied with the YA JEM code in two different scenarios by (i)
accounting for the medium induced virtuality ∆Q2 transferred to the leading parton from the medium, and
(ii) by altering the infrared sector in the Borghini-Wiedemann approach. The results of our simulations are
compared to experimental jet data measured by the CMS experiment in PbPb and pp collisions at a center-ofmass energy of 2.76 TeV. Though both scenarios qualitatively describe the shape and main physical features
of the FFs, the ratios are in much better agreement with the first scenario. Results are presented for the Monte
Carlo FFs obtained for different parton flavours (quark and gluon) and accounting exactly, or not, for the
experimental jet reconstruction biases.
1
Department of Physics, P.O. Box 35, FI-40014 University of Jyväskylä, Jyväskylä, Finland
Sorbonne Université, UPMC Univ Paris 06, UMR 7589, LPTHE, F-75005, Paris, France
CNRS, UMR 7589, LPTHE, F-75005, Paris, France
4
Postal address: LPTHE tour 13-14, 4e` me e´ tage, UPMC Univ Paris 06, BP 126, 4 place Jussieu, F-75252 Paris Cedex 05 (France)
5
e-mail: [email protected], [email protected]
6
Department of Physics, P.O. Box 35, FI-40014 University of Jyväskylä, Jyväskylä, Finland
7
Helsinki Institute of Physics, P.O. Box 64, FI-00014 University of Helsinki, Helsinki, Finland
8
e-mail: [email protected], [email protected]
2
3
1 Introduction
Experiments at the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) have observed
the formation of a Quark-Gluon Plasma (QGP) in AuAu and PbPb collisions respectively. Highly virtual quarks
and gluons (generically called partons) lose energy as they traverse the QGP, resulting in the suppression of high
transverse momentum leading hadrons [1–4] and jets [5, 6] as well as in the modification of jet fragmentation
functions and jet shapes [7–9], observed in central heavy-ion collisions.
In the vacuum, the production of highly virtual partons issuing from a hard scattering of two partons from
the incoming protons results in a spray of collimated hadrons observed in the final-state of the collision. The
evolution of successive splittings q(¯
q ) → q(¯
q )g, g → gg and g → q q¯ (q, q¯ and g label quark, antiquark
and gluon respectively) inside the parton shower prior to hadronization can be computed analytically from
perturbative QCD calculations resumming collinear and infrared divergences [10] or, alternatively, in terms of
Monte Carlo (MC) formulations of the parton branching process such as the PYSHOW algorithm implemented
in PYTHIA [11, 12]. In nucleus-nucleus (A-A) collisions, partons produced in the hard scatterings of two
partons from the nuclei propagate through the hot/dense QCD medium also produced in such collisions and
their branching pattern is changed by interacting with the color charges of the deconfined QGP [13]. As a
consequence, additional medium-induced soft gluon radiation is produced in A-A collisions, which leads for
instance to the suppression of high-pT hadroproduction [14–16] and a plethora of other jet modifications (see
e.g. [17]). In the past few years, MC codes for in-medium shower simulations developed for hadronic collisions
have also become available [18–22]. They have been based on the success of MC shower simulations in the
vacuum such as PYTHIA and HERWIG [23].
The parton-to-hadron jet fragmentation functions (FFs), dN
dξ ≡ zDi→h (z, Q) with ξ = ln(1/z), encode the
probability that a parton i fragments into a hadron h carrying a fraction z of the parent parton’s momentum. In
this paper, we compute the medium-modified FFs and the FF ratio of the fragment yield with YA JEM, where
the medium itself is described by a 3-d hydrodynamical evolution [19, 20]. We compare our results with recent
PbPb and pp CMS data collected at center-of-mass energy 2.76 TeV [9]. In the first scenario of the YA JEM
code, it is mainly assumed that the cascade of branching partons traverses a medium which, consistently with
standard radiative loss pictures, is characterized by a local transport coefficient qˆ which measures the virtuality
per unit length transferred from the medium to the leading parton. Hence, the virtuality of the leading parton
is increased by the integrated amount “∆Q2 ” which opens up the phase space and leads to a softer shower.
The second scenario is based on the Borghini-Wiedemann (BW) model [24], where the singular part of the
branching kernels in the medium is enhanced by a factor 1 + fmed , such that Pa→bc = (1 + fmed )/z + O(1),
where a → bc describes the possible QCD parton branchings, i.e. q(¯
q ) → q(¯
q )g and g → gg with g → q q¯
unchanged. In this case, the softening of the shower is described by the larger amount of medium-induced
soft gluons (fmed > 0) as compared to the vacuum (fmed = 0). In both scenarios, the final parton-to-hadron
transition takes place in the vacuum, using the Lund model [25], for hadronization scales below Q0 = 1 GeV.
For the purpose of a realistic comparison of YA JEM and PYTHIA 6 with the CMS data, the FF analysis is
carried out by following the CMS analysis closely. Jets are reconstructed with the anti-kt algorithm [26, 27]
with a resolution parameter R = 0.3. The clustering analysis is limited to charged particles with pt > 1
GeV inside the jet cone where PT ≥ 100, 120, 150 GeV are required for jets (i.e. PT stands for the jet
1
HUPD1405
Study of an anomalous tau lepton decay using
a chiral Lagrangian with vector mesons
Daiji Kimura
arXiv:1411.1961v1 [hep-ph] 7 Nov 2014
Ube National College of Technology, Ube Yamaguchi 755-8555, Japan
Takuya Morozumi, Hiroyuki Umeeda
Graduate School of Science, Hiroshima University Higashi-Hiroshima 739-8526, Japan
Abstract
The hadronic tau decay τ − → ντ ηπ − π 0 occurs through V-A weak current. In this decay mode,
the vector current contribution is intrinsic parity violating and the axial current contribution is
G parity violating. The latter contribution is suppressed due to tiny isospin breaking. We have
computed both vector and axial vector form factors using a chiral Lagrangian with vector mesons
including the effect of isospin breaking and intrinsic parity violation. A numerical result of the
invariant mass distribution is shown and the structure of ρ resonance can be seen in the distribution
with respect to Mπ− π0 .
1
IFT-UAM/CSIC-14-113
FTUAM-14-45
Nucl.Phys.B
Proc.Suppl.
arXiv:1411.1940v1 [hep-ph] 7 Nov 2014
Nuclear Physics B Proceedings Supplement 00 (2014) 1–7
Electroweak chiral Lagrangian with a light Higgs
and γγ → ZL ZL , WL+WL− scattering at one loop
R.L. Delgado, A. Dobado,
Departamento de F´ısica Teórica I, UCM,
Universidad Complutense de Madrid, Avda. Complutense s/n, 28040 Madrid, Spain
M.J. Herrero and J.J. Sanz-Cillero
Departamento de F´ısica Teórica and Instituto de F´ısica Teórica, IFT-UAM/CSIC
Universidad Autónoma de Madrid, C/ Nicolás Cabrera 13-15,
Cantoblanco, 28049 Madrid, Spain
Abstract
In these proceedings we provide a brief summary of the findings of a previous article where we have studied the photon-photon
scattering into longitudinal weak bosons within the context of the electroweak chiral Lagrangian with a light Higgs, a low-energy
effective field theory including a Higgs-like scalar singlet and where the electroweak would-be Goldstone bosons are non-linearly
realized. We consider the relevant Lagrangian up to next-to-leading order in the chiral counting, which is explained in some
detail here. We find that these amplitudes are ultraviolet finite and the relevant combinations of next-to-leading parameters (cγ
and a1 − a2 + a3 ) do not get renormalized. We propose the joined analysis of γγ–scattering and other photon related observables
(Γ(h → γγ), S –parameter and the γ∗ → WL+ WL− and γ∗ → hγ electromagnetic form-factors) in order to separate and determine each
chiral parameter. Moreover, the correlations between observables provided by the NLO computations would lead to more stringent
bounds on the new physics that is parametrized by means of this effective Lagrangian. We also show an explicit computation of
the γγ–scattering up to next-to-leading order in the S O(5)/S O(4) minimally composite Higgs model.
Keywords:
Higgs Physics, Beyond Standard Model, Chiral Lagrangians
Standard Model (BSM) effects in the electroweak
(EW) sector.
In these proceedings we discuss some of the findings in a previous work [2]. Therein we studied the
processes γγ → ZL ZL and γγ → WL+ WL− in the context of a general EW low-energy effective field theory (EFT), which we will denote as Electroweak Chiral Lagrangian with a light Higgs (ECLh), with the EW
would-be Goldstone bosons (WBGBs) denoted here by
wa and non-linearly realized. In addition to be more
general, this non-linear representation seems to be more
appropriate in the case of strong interactions in the
EW sector, as it is the case in Quantum Chromody-
1. γγ–scattering as a probe into new physics
Two years ago the Large Hadron Collider (LHC) discovered a new particle, most likely a scalar, with mass
mh ≈ 125 GeV [1] and couplings so far compatible
with what one would expect for the Standard Model
(SM) Higgs boson. We are therefore in a scenario with
small deviations from the SM and, apparently, a large
mass gap (as no new particle has shown up below the
TeV). Thus, the effective field theory (EFT) framework
seems to be the most convenient one to confront current
experimental data and to explore possible beyond
1
Why should we care about the top quark Yukawa coupling?1
Fedor Bezrukov1, 2, 3, ∗ and Mikhail Shaposhnikov4, †
1
CERN, CH-1211 Genève 23, Switzerland
Physics Department, University of Connecticut, Storrs, CT 06269-3046, USA
3
RIKEN-BNL Research Center, Brookhaven National Laboratory, Upton, NY 11973, USA
4
´
Institut de Théorie des Phénomènes Physiques, Ecole
Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
2
We give an answer to the question formulated in the title.
arXiv:1411.1923v1 [hep-ph] 7 Nov 2014
I.
INTRODUCTION
In the Spring of 2014 Valery Rubakov was visiting
CERN and joined a bunch of theorists for a lunch at
the CERN canteen. As often happens, the conversation
turned to the future of high energy physics: what kind
of questions should be answered and what kind of experiments should be done. Valery was arguing for the
high energy frontier which would allow to search for new
physics, whereas the authors of this article brought attention to the precision measurements of the top quark
Yukawa coupling. We remember Valery asking: “Why
should we care about the top quark Yukawa coupling?”
Because of some reasons the interesting discussion was
interrupted and we did not have a chance to explain our
point of view in detail. We use this opportunity to congratulate Valery with his coming jubilee and give an answer to his question in writing. We apologise to Valery
for describing in this text a number of well-known to him
facts, which we included to make this essay accessible to
a wider audience.
II.
STANDARD MODEL AND THE SCALE OF
NEW PHYSICS
After the discovery of the Higgs boson at the LHC
the Standard Model (SM) became a complete theory in
the sense that all the particle degrees of freedom that
it contains theoretically have been found experimentally.
Moreover there are no convincing deviations from the SM
in any type of high energy particle physics experiments.
This raises a number of questions: “Have we got at last
the ultimate theory of Nature?” and “If not, where we
should search for new physics?”
The answer to the first question is well known and it
is negative. The reasons are coming from the observations of neutrino oscillations, absent in the SM, and from
1
∗
†
To be published in a special edition of the Journal of Experimental and Theoretical Physics in honor of the 60th birthday of
Valery Rubakov.
[email protected]
[email protected]
cosmology—the SM cannot accommodate dark matter
and baryon asymmetry of the Universe. The last but not
the least is the inflation, or, to stay strictly on the experimental evidence side, the flatness and homogeneity of the
Universe at large scales and the origin of the initial density perturbations. On a more theoretical side, the list of
the drawbacks of the SM is quite long and includes incorporation of gravity into a quantum theory, the hierarchy
problem, the strong CP-problem, the flavour problem,
etc., etc.
The answer to the second question is not known. What
is theoretically clear, is that some type of new physics
must appear near the Planck energies MP = 2.435 × 1018
GeV, where gravity becomes important, but these energies are too high to be probed by any experimental
facility. The naturalness arguments put the scale of new
physics close to the scale of electroweak symmetry breaking (see, e.g. [1, 2]), but it is important to note that the
SM by itself is a consistent quantum field theory up to the
very high energies exceeding the Planck mass by many
orders of magnitude, where it eventually breaks down
due to the presence of Landau-poles in the scalar selfinteraction and in U(1) gauge coupling.
As for the experimental evidence in favour of new
physics, it does not give any idea of its scale: the neutrino oscillations can be explained by addition of Majorana leptons with the masses ranging from a fraction of
electron-volt to 1016 GeV, the mass of particle candidates
for dark matter discussed in the literature vary by at least
30 orders of magnitude, the mass of Inflaton can be anywhere from hundreds of MeV to the GUT scale, whereas
the masses of new particles responsible for baryogenesis
can be as small as few MeV and as large as the Planck
scale.
As we are going to argue in this paper at the present
moment the only quantity which can help us to get an
idea about the scale of new physics is the top Yukawa coupling yt . It may happen that the situation will change
in the future: the signals of new physics may appear at
the second stage of the LHC, or the lepton number violation will be discovered, or anomalous magnetic moment
of muon will convincingly be out of the SM prediction,
or something unexpected will show up.
One Right-handed Neutrino to Generate Complete Neutrino
Mass Spectrum in the Framework of NMSSM
Yi-Lei Tang
Institute of Theoretical Physics, Chinese Academy of Sciences,
arXiv:1411.1892v1 [hep-ph] 7 Nov 2014
and State Key Laboratory of Theoretical Physics,
P. O. Box 2735, Beijing 100190, China∗
Abstract
The see-saw mechanism is usually applied to explain the lightness of neutrinos. The traditional
see-saw mechanism introduces at least two right-handed neutrinos for the realistic neutrino spectrum. In the case of supersymmetry, loop corrections can also contribute to neutrino masses, which
lead to the possibility to generate the neutrino spectrum by introducing just one right-handed neutrino. To be realistic, MSSM suffers from the µ problem and other phenomenological difficulties, so
we extend NMSSM (the MSSM with a singlet S) by introducing one single right-handed neutrino
superfield (N) and relevant phenomenology is discussed.
PACS numbers:
∗
Electronic address: [email protected]
1
arXiv:1411.1877v1 [hep-ph] 7 Nov 2014
Neutrinoless double beta decay mediated by the
neutrino magnetic moment
Marek G´
o´
zd´
z and Wieslaw A. Kami´
nski
Department of Informatics, Maria Curie-Sklodowska University
ul. Akademicka 9, 20-033 Lublin, Poland
Abstract. We present a new channel of the neutrinoless double beta decay. In this
scenario neutrinos not only oscillate inside the nucleus but also interact with an external
non-uniform magnetic field. We assume that the field rotates about the direction of
motion of the neutrino and show, that for a certain speed of rotation the half-life of
the 0ν2β decay may be significantly lowered.
PACS numbers: 12.90.+b, 13.40.Em, 14.60.Pq
Keywords: neutrinoless double beta decay, neutrino magnetic moment, neutrino
oscillations
Submitted to: Phys. Scr.
1. Introduction
Neutrinos, although weakly, interact with other particles, and therefore propagation and
oscillation of these particles in vacuum differs from that in matter. This is known as the
Mikheyev – Smirnov – Wolfenstein effect (MSW) [1] and has recently been observed by
the Super-Kamiokande Collaboration as an asymmetry in the oscillation rate between
zenith and nadir neutrinos [2]. This effect is based on the fact, that the components of
‘ordinary’ matter, i.e., electrons, protons, and neutrons, interact with electron neutrinos
via charged as well as neutral currents. Muon and tau neutrinos, on the other hand,
cannot interact with the electrons, thus participate in the neutral current processes
only. This results in an asymmetry in the forward scattering amplitude of different
neutrino flavours, effectively shifting the neutrino oscillation parameters. So regular
matter distinguishes between electron and other neutrino flavours.
Weak interactions are not the only factors that may affect neutrino propagation
and oscillations. Despite being electrically neutral, neutrinos, according to the Standard
Model, should exhibit electromagnetic properties. In the second order 1-loop process
in which ν W ± `∓ neutrino magnetic moment has been estimated by Fuijkawa and
Shrock to be 3.2×10−19 (mν )µB [3], which yields for mν = 0.05 eV the value 1.6×10−20 µB
ECTP-2013-20
and
WLCAPP-2013-17
Thermodynamics and higher order moments in SU(3) linear
σ-model with gluonic quasi-particles
Abdel Nasser
TAWFIK∗
arXiv:1411.1871v1 [hep-ph] 7 Nov 2014
Egyptian Center for Theoretical Physics (ECTP),
Modern University for Technology and Information (MTI), 11571 Cairo, Egypt and
World Laboratory for Cosmology And Particle Physics (WLCAPP), Cairo, Egypt
Niseem MAGDY
World Laboratory for Cosmology And Particle Physics (WLCAPP), 11571 Cairo, Egypt and
Brookhaven National Laboratory (BNL) - Department of
Physics P.O. Box 5000, Upton, NY 11973-5000, USA
∗
http://atawfik. net/
1
Abstract
In framework of linear σ-model (LSM) with three quark flavors, the chiral phase-diagram at finite temperature and density is investigated. At temperatures higher than the critical temperature
(Tc ), we added to LSM the gluonic sector from the quasi-particle model (QPM), which assumes that
the interacting gluons in the strongly interacting matter, the quark-gluon plasma (QGP), are phenomenologically the same as non-interacting massive quasi-particles. The dependence of the chiral
condensates of strange and non-strange quarks on temperature and chemical potential is analysed.
Then, we have calculated the thermodynamics in the new approach (combination of LSM and QPM).
Confronting the results with recent lattice QCD simulations shows an excellent agreement in almost
all thermodynamic quantities. The first and second order moments of particle multiplicity are studied
in dependence on the chemical potential but at fixed temperature and on the chemical potential but
at fixed temperature. These are implemented in characterizing the large fluctuations accompanying
the chiral phase-transition. The results of first and second order moments are compared with the
SU(3) Polyakov linear σ-model (PLSM). Also, the resulting phase-diagrams deduced in PLSM and
LSM+QPM are compared with each other.
PACS numbers: 12.39.Fe, 12.38.Aw, 12.38.Mh
Keywords: Chiral Lagrangian, Quark confinement, Quark-gluon plasma
2
KEK-TH-1776
UT-Komaba/14-6
Dynamic Critical Exponent from One- and Two-Particle Irreducible 1/N
Expansions of Effective and Microscopic Theories
arXiv:1411.1867v1 [hep-ph] 7 Nov 2014
Osamu Morimatsu
KEK Theory Center, IPNS,
High Energy Accelerator Research Organization (KEK),
1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan
Department of Physics, Faculty of Science, University of Tokyo,
7-3-1 Hongo Bunkyo-ku Tokyo 113-0033, Japan and
Department of Particle and Nuclear Studies,
Graduate University for Advanced Studies (SOKENDAI),
1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
Hirotsugu Fujii
Institute of Physics, University of Tokyo, Tokyo 153-8902, Japan
Kazunori Itakura
KEK Theory Center, IPNS, High Energy Accelerator Research Organization (KEK),
1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan and
Department of Particle and Nuclear Studies,
Graduate University for Advanced Studies (SOKENDAI),
1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
Yohei Saito
KEK Theory Center, IPNS,
High Energy Accelerator Research Organization (KEK)
1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan
The dynamic critical exponent z is studied in two different theoretical frameworks: one is the
effective theory of a time-dependent Ginzburg-Landau model, i.e., model A in the classification of
Hohenberg and Halperin, and the other is the microscopic finite-temperature field theory in the
imaginary time formalism. Taking an O(N ) scalar model as an example and carrying out the
1/N expansion up to the next-to-leading order (NLO) in the one-particle-irreducible (1PI) and twoparticle-irreducible (2PI) effective actions, we compare the low-energy and low-momentum (infrared)
behavior of the two-point functions in the two theories. At the NLO of the 1PI 1/N expansion the
infrared behavior of the two-point functions in the effective and microscopic theories is very much
different from each other: it is dominated by the diffusive mode with, z = 2 + 3π4 2 N1 , in model A,
16 1
while in the microscopic theory it is dominated by the propagating mode with z = 1 − 3π
2 N or
32 1
z = 2 − 3π
2 N depending on whether the kinematics is relativistic or nonrelativistic. In contrast, at
the NLO of the 2PI 1/N expansion, we find that the two theories become equivalent for describing
the infrared behavior of the two-point function in the sense that the self-consistent equation for the
two-point function, the Kadanoff-Baym equation, has exactly the same form both in the microscopic
and effective theories. At this point, the relativistic or nonrelativistic kinematics of the bare two
point function in the microscopic theory becomes irrelevant in the critical dynamics. This implies
that the diffusive mode with z = 2 + O(1/N ) becomes dominant at low energies and momenta even
in the microscopic theory at the NLO of the 2PI 1/N expansion, though we do not explicitly solve
the Kadanoff-Baym equation. We also try to improve the estimate of the dynamic critical exponent
of model A given in the literature, at the NLO of the strict 1/N expansion. This calculation can
be regarded as an approximation to the 2PI NLO calculation of the dynamic critical exponent not
only in the effective theory but also in the microscopic theory. By incorporating the static 2PI
correlations into the two-point function we identify the infrared logarithmic term with respect to
energy or momentum in the 1/N NLO self-energy, from which we determine the critical exponent,
z. The obtained critical exponent is slightly smaller than the previous known result and its N
dependence is also milder than the previous one.
2
I.
INTRODUCTION
Relaxation to the equilibrium state of a system at a critical point becomes extremely slow and shows a
universal behavior. Recently, such dynamic critical phenomena have been receiving much interests in various
fields of physics from condensed matter physics to cosmology [1–3]. The dynamic critical phenomena have
successfully been described by effective theories [1, 4–6], and have been classified into several subclasses
from the static universal classes according to the symmetries of the order parameters and whether there are
couplings to other conserved quantities or not [4]. In these effective theories diffusive motions are assumed
for the order parameters at the tree level and then nonlinear interactions among the order parameters are
included together with the interactions of the order parameters and the conserved quantities. In principle
both the effective and microscopic theories should describe critical phenomena equally well, if one can take
into account contributions relevant to dynamic critical phenomena in each theory. However, it is known, for
instance, that the 1/N expansion in the standard method of the one-particle-irreducible (1PI) effective action
leads to different results for the dynamic critical exponent in the effective and microscopic theories [7–12].
Thus, microscopic understandings of dynamic critical phenomena, in particular the generation of the diffusive
mode, have not been achieved and still remain a challenge [13–15].
The method of the two-particle-irreducible (2PI) effective action [16–18] has recently attracted much attention [19–22]. In this method, self-energy corrections for the two-point function are first summed up and
then the expansion is carried out in terms of the full two-point function. This is in contrast to the standard
method of the 1PI effective action, where the expansion is in terms of the free two-point function. The method
of the 2PI effective action provides us with a way of systematic resummation of the perturbative expansion.
Therefore, as was suggested in Ref. [15], it is expected to take into account the secular effects of collisions
in the microscopic theory which are considered to be responsible for the diffusive behavior of the two-point
function at low energies and momenta.
According to the dynamic scaling hypothesis [23–26], the inverse of the retarded two-point function at the
critical point, G(p, p0 )−1 , has the form
p0
G(p, p0 )−1 = |p|2−η g
,
(1)
|p|z
where η (z) is the static (dynamic) critical exponent and p0 (p) is the energy (momentum). This relation
implies that the mode energy scales with the momentum as p0 ∼ |p|z at the critical point.
For low p0 (p), G(p, p0 )−1 is analytic in p0 (p)
(
a0 |p|2−η + a1 p0 |p|2−η−z + a2 p20 |p|2−η−2z + · · · (low p0 ) ,
(2)
G(p, p0 )−1 =
(2−η)/z
(2−η−1)/z
b1 p 0
+ b2 |p|p0
+ ···
(low |p|) ,
which constrains the asymptotic behavior of the scaling function, g(x), to be
(
a0 + a1 x + a2 x2 + · · ·
(small x) ,
g(x) =
b1 x(2−η)/z + b2 x(1−η)/z + · · · (large x) .
Therefore, while the static critical exponent, η, can be read off from G(p, 0)−1 , the dynamic critical exponent,
z, can be obtained from either G(0, p0 )−1 or ∂G(p, p0 )−1 /∂p0 |p0 =0 together with the knowledge of η.
The purpose of the present paper is twofold. Firstly, we would like to clarify the relation between two
descriptions of the dynamic critical phenomena, i.e. in terms of the effective theory and in terms of the
microscopic theory, paying special attention to the diffusive mode. Thereby, we would like to resolve the
confusions sometimes seen in the literature. We employ a simple time-dependent Ginzburg-Landau (TDGL)
model [27] or model A in the classification of Ref. [4] for the effective theory and the imaginary-time formalism
of the field theory at finite temperature [28–31] for the microscopic theory. Taking an O(N ) scalar model
as an example and carrying out the 1/N expansion up to the next-to-leading order (NLO) in the 1PI and
2PI effective actions, we compare the low-energy and low-momentum behavior of the response function in
the effective theory and of the retarded Green’s function in the microscopic theory. We show that two
descriptions are equivalent at the NLO of the 2PI 1/N expansion, i.e. the self-consistent equation for the twopoint function, the Kadanoff-Baym equation, is exactly the same in the effective and microscopic theories,
CALT-TH-2014-160
arXiv:1411.1772v1 [hep-ph] 6 Nov 2014
Yukawa Bound States of a Large Number of Fermions
Mark B. Wise and Yue Zhang
Walter Burke Institute for Theoretical Physics,
California Institute of Technology, Pasadena, CA 91125
[email protected],
[email protected]
Abstract: We consider the bound state problem for a field theory that contains a Dirac
fermion χ that Yukawa couples to a (light) scalar field φ. We are interested in bound states
with a large number N of χ particles. A Fermi gas model is used to numerically determine
the dependence of the radius R of these bound states on N and also the dependence of
the binding energy on N . Since scalar interactions with relativistic χ’s are suppressed two
regimes emerge. For modest values of N the state is composed of non-relativistic χ particles.
In this regime as N increases R decreases. Eventually the core region becomes relativistic
and the size of the state starts to increase as N increases. As a result, for fixed Yukawa
coupling and χ mass, there is a minimum sized state that occurs roughly at the value of
N where the core region first becomes relativistic. As an application to dark matter, our
analysis offers the possibility of having a supermassive thermal DM candidate. We also
compute an elastic scattering form factor that can be relevant for direct detection if the dark
matter is composed of such χ particles.
1
arXiv:1411.1765v1 [hep-ph] 6 Nov 2014
Right-handed neutrino production rate at T > 160 GeV
I. Ghisoiua and M. Laineb
a Department
of Physics and Helsinki Institute of Physics,
University of Helsinki, P.O.Box 64, FI-00014 Helsinki, Finland
b Institute
for Theoretical Physics, Albert Einstein Center, University of Bern,
Sidlerstrasse 5, CH-3012 Bern, Switzerland
Abstract
The production rate of right-handed neutrinos from a Standard Model plasma at a temperature above a hundred GeV has previously been evaluated up to NLO in Standard Model
couplings (g ∼ 2/3) in relativistic (M ∼ πT ) and non-relativistic regimes (M ≫ πT ), and
up to LO in an ultrarelativistic regime (M <
∼ gT ). The last result necessitates an all-orders
resummation of the loop expansion, accounting for multiple soft scatterings of the nearly
light-like particles participating in 1 ↔ 2 reactions. In this paper we suggest how the regimes
can be interpolated into a result applicable for any right-handed neutrino mass and at all
temperatures above 160 GeV. The results can also be used for determining the lepton number
washout rate in models containing right-handed neutrinos. Numerical results are given in a
tabulated form permitting for their incorporation into leptogenesis codes. We note that due
1/2
to effects from soft Higgs bosons there is a narrow intermediate regime gT <
∼M <
∼ g T in
which our interpolation is phenomenological and a more precise study would be welcome.
November 2014
arXiv:1411.1899v1 [cs.DL] 7 Nov 2014
Intriguing Trends in Nuclear Physics Articles Authorship
B. Pritychenkoa
National Nuclear Data Center, Brookhaven National Laboratory, Upton, NY
11973-5000, U.S.A.
a
The increase in authorship of nuclear physics publications has been investigated using
the large statistical samples. This has been accomplished with nuclear data mining of
nuclear science references (NSR) and experimental nuclear reaction (EXFOR) databases.
The results of this study will be discussed and conclusions will be given.
1. Introduction
The authorship in physics publications is a very interesting topic that has been extensively discussed in Physics Today in recent years [ 1, 2]. The journal readers disclosed
many interesting observations that, unfortunately, are often based on rather limited statistics. “The ongoing obsession with citation count as the marker of achievement” [ 2], as
well as pressures to “publish or perish” are often cited as reasons for increases of authors
number per paper [ 3]. Obviously, these reasons contribute to the presently-observed
author list increase, and these findings are supported by R. Heras [ 4]. At the same
time, research authorship and its evolution over the years are complex phenomena that
require extensive studies of scientific publications and broad discussions. To extend the
scope of the above-mentioned studies, I will investigate the authorship of nuclear physics
articles using the statistically-significant data samples extracted from the modern low-,
and intermediate-energy nuclear physics databases maintained by the National Nuclear
Data Center (NNDC) [ 5].
2. Nuclear Physics Databases
Collection and storage of nuclear bibliography materials is a foundation for nuclear
data compilations and evaluations. These extensive collections were assembled by nuclear data compilers over the past 50-60 years and represent a treasure trove for the scientists, who search these databases for nuclear physics publications and relevant data.
In this work, I would consider the NSR (http://www.nndc.bnl.gov/nsr) and EXFOR
(http://www.iaea.org/exfor) databases [ 6, 7] that contain records of more than 215000
publications, 92600 individual authors, and 20000 cross nuclear reaction measurements.
These databases provide a complete coverage of nuclear physics publications, and are
relatively-clean from the high-energy physics papers, where the authorship rules are very
different [ 1, 8].
Those maintained by the NNDC, NSR database [ 6] is a prime source of nuclear bib-
Deformation effects on the coexistence between neutron-proton and particle like
pairing in N=Z medium mass nuclei
Danilo Gambacurta∗
Istituto Nazionale di Fisica Nucleare, Sezione di Catania, Via S. Sofia 64, I-95123 Catania, Italy and
GANIL, CEA/DSM and CNRS/IN2P3, Boˆıte Postale 55027, 14076 Caen Cedex, France
Denis Lacroix†
arXiv:1411.1891v1 [nucl-th] 7 Nov 2014
Institut de Physique Nucléaire, IN2P3-CNRS, Université Paris-Sud, F-91406 Orsay Cedex, France
A model combining self-consistent mean-field and shell-model techniques is used to study the
competition between particle like and proton-neutron pairing correlations in fp-shell even-even selfconjugate nuclei. Results obtained using constant two-body pairing interactions as well as more
sophisticated interactions are presented and discussed. The standard BCS calculations are systematically compared with more refined approaches including correlation effects beyond the independent
quasi-particle approach. The competition between proton-neutron correlations in the isoscalar and
isovector channels is also analyzed, as well as their dependence on the deformation properties. Besides the expected role of the spin-orbit interaction and particle number conservation, it is shown
that deformation leads to a reduction of the pairing correlations. This reduction originates from
the change of the single-particle spectrum and from a quenching of the residual pairing matrix elements. The competition between isoscalar and isovector pairing in the deuteron transfer is finally
addressed. Although a strong dependence the isovector pairing correlations with respect to nuclear
deformation is observed, they always dominate over the isoscalar ones.
PACS numbers: 21.10.Dr,21.30.Fe , 21.60.-n, 27.40.+z,21.60.Jz
Keywords: Microscopic theory, proton-neutron pairing
I.
INTRODUCTION
Although the role of pairing correlations in nuclei was
introduced more than 60 years by Bohr, Mottelson and
Pines [1] and they dictate many nuclear properties [2, 3],
some aspects of pairing remain unclear. For instance, the
precise role of the neutron (n)-proton (p) pairing in nuclei
still challenges both theoretical and experimental nuclear
physics [4–10] (see Ref. [11] for a recent review). The
effect of correlation between nucleons of different spin
and isospin, is expected to be more pronounced in selfconjugate nuclei. From an experimental point of view,
high intensity radioactive beams will offer new possibilities to study the importance of isoscalar (T = 0) and
isovector (T = 1) pairing interaction between protons
and neutrons along the N = Z line. The role of isovector proton-neutron (p-n) pairing correlations has been
recently pointed out by analyzing the relative energies of
the T=0 and T=1 states in even-even and odd-odd nuclei
[12] and the T = 0 band in 74 Rb [13]. The analysis based
on these results provides evidences of the existence of a
neutron-proton isovector pair field but does not support
the existence of the isoscalar one. Conjointly, recent experiments seem to manifest the possibility to observe exotic structure of aligned pairs [9] that could be explained
in terms of isoscalar p-n pairing correlations.
∗ Electronic
† Electronic
address: [email protected]
address: [email protected]
From a theoretical point of view, several frameworks
have been proposed to incorporate p-n pairing correlations in microscopic models. Many works devoted to the
study of the competition between isoscalar and isovector pairing, have been performed in solvable models (see
for example [14–19]). Mean-field approaches, generally
only incorporate particle-like pairing correlations. Extensions to include p-n correlations have been already
proposed some times ago [4] and sometimes applied in
the Hartree-Fock Bogolyubov (HFB) approach [20, 21].
Most often, these approaches lead to a non-coexistence
of particle-like and particle unlike pairing that is further
supported by the analytical work in Refs. [22, 23]. It is
worth mentioning that such coexistence has been found
away from stability in some exotic situations [24]. Alternatively, shell-model calculations starting from a simplified pairing Hamiltonian can go beyond the independent quasi-particle picture and provide a particle number
conserving framework able to attack the pairing problem
including all spin/isospin channels. Beyond mean-field
studies have been recently performed to study the competition between T = 0 and T = 1 pairing in spherical
nuclei [25], to understand the origin of the Wigner energy [26, 27] to probe the existence of quarteting [28–31],
to describe spin-aligned pairs [32] or deuteron transfer
properties in N=Z nuclei [33].
It is worth mentioning that deformation has sometimes been included using schematic [34] or more realistic
Hamiltonian [35]. The aim of the present work is tomake
a precise study of the role of deformation on particlelike and p-n pairing by using the following strategy. A
Effect of initial fluctuations on the collective flow in intermediate-energy heavy ion
collisions
J. Wang,1, 2 Y. G. Ma∗ ,1, 3 G. Q. Zhang,1 and W. Q. Shen1, 3
arXiv:1411.1812v1 [nucl-th] 7 Nov 2014
1
Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
Shanghai Tech University, Shanghai 200031, China
A systemical analysis of the initial fluctuation effect on the collective flows for Au+Au at 1A GeV
has been presented in the framework of Isospin-dependent Quantum Molecular Dynamics model
(IQMD), and a special focus on the initial fluctuation effect on the squeeze-out is emphasized. The
flows calculated by the participant plane reconstructed by the initial geometry in coordinate space
are compared with those calculated by both the ideal reaction plane and event plane methods. It is
found that initial fluctuation weakens squeeze-out effect, and some discrepancies between the flows
extracted by the above different plane methods appear which indicate that the flows are affected
by the evolution of dynamics. In addition, we found that the squeeze-out flow is also proportional
to initial eccentricity. Our calculations also qualitatively give the similar trend for the excitation
function of the elliptic flow of the FOPI experimental data. Finally we address the nucleon number
scaling of the flows for light particles. Even though initial fluctuation decreases the ratio of v4 /v22 as
well as v3 /(v1 v2 ) a lot, all fragments to mass number 4 keep the same curve and shows independent
of transverse momentum.
PACS numbers: 25.75.Ld, 24.10.i
I.
INTRODUCTION
Recent relativistic heavy-ion collision (HIC) studies
have recognized the importance of the initial fluctuations
on the various order of flows [1–13]. For instance, the
origin of the triangular flow v3 and higher harmonics is
fluctuation in initial conditions [5, 9, 14]. In particular,
v3 vanishes, if the system starts with a smooth almondshaped initial state [5]. It also shows the ratio of elliptic flow to eccentricity (v2 /ε2 ) is sensitive to the initial
fluctuation. By now, studies on the initial fluctuation
effects are only limited in relativistic heavy-ion collision.
At these energies, the initial fluctuation can be followed
by hydrodynamic expansion and result in the long-range
azimuthal correlations (or the anisotropy flows). Its energy dependence is thought as one of important observables to study various aspects of the QCD phase diagram
in the beam energy scan (BES) program at RHIC [15–
18]. In intermediate energy HIC, no systematic study
for the initial fluctuation effects on the collective flow
has been presented except a brief report appeared by the
same authors of the present work [19]. Also, the relationship between the eccentricity and squeeze-out (negative
elliptic flow) is not yet reported to our knowledge. In
contrast with relativistic energy HIC, the time scale of
collision dynamics is larger (from tens of fm/c to hundreds of fm/c) in intermediate energy HIC, which may
allow the other factors to develop and smear the longrange azimuthal correlations originating from the initial
fluctuation. It is then worth addressing how the initial
∗ Corresponding
author. E-mail address: [email protected]
fluctuation affects on the collective flow in intermediate
energy domain.
In this paper, the collective flows are calculated in a
framework of a nuclear transport model, namely Isospin
Quantum Molecular Dynamics (IQMD), which allows the
generation of events with event-by-event fluctuating initial conditions. To explore the effects of the initial fluctuation, we study the flows as functions of centrality,
transverse component of four velocity and rapidity. Flow
results with respect to different reaction plane determinations are compared with the experimental data. We
also try to reproduce experimental excitation function of
elliptic flow with our simulations. In addition, the relationship of elliptic flow versus eccentricity is discussed in
different centralities. The EOS dependence of the collective flow is also presented. At the end, we will focus
on phenomenology of mass-number scaling behavior of
different harmonic flows and check the initial fluctuation
effect on scaling behavior.
The paper is organized in the following way. A brief description of the IQMD model is introduced in Sec. II. The
initial fluctuation is described in Sec. III. The methodology of the flow calculations is presented in Sec. IV. The
results and discussion are presented in Sec. V. Finally,
summary is given in Sec. VI.
II.
BRIEF DESCRIPTION OF IQMD
The Quantum Molecular Dynamics (QMD) approach
is an n-body theory to simulate heavy ion reaction at
intermediate energies. It contains several major parts:
the initialization of the target and the projectile nucleons, the spread of nucleons in the effective potential, the
Preprint typeset in JINST style - HYPER VERSION
Radiopurity assessment of the tracking readout for
the NEXT double beta decay experiment
V. Álvarez,a I. Bandac,b A.I. Barrado,c A. Bettini,b,d F.I.G.M. Borges,e M. Camargo, f
S. Cárcel,a S. Cebrián,b,g∗A. Cervera,a C.A.N. Conde,e E. Conde,c T. Dafni,b,g J. Díaz,a
R. Esteve,h L.M.P. Fernandes,e M. Fernández,h P. Ferrario,a A.L. Ferreira,i
E.D.C. Freitas,e V.M. Gehman,i A. Goldschmidt,i H. Gómez,b,g J.J. Gómez-Cadenas,a†
D. González-Díaz,b,g R.M. Gutiérrez, f J. Hauptman,k J.A. Hernando Morata,l
D.C. Herrera,b,g F.J. Iguaz,b,g I.G. Irastorza,b,g L. Labarga,m A. Laing,a I. Liubarsky,a
D. Lorca,a M. Losada, f G. Luzón,b,g A. Marí,h J. Martín-Alboa A. Martínez,a
G. Martínez-Lema,l T. Miller,i F. Monrabal,a M. Monserrate,a C.M.B. Monteiro,e
F.J. Mora,h L.M. Moutinho,i J. Muñoz Vidal,a M. Nebot-Guinot,a D. Nygren,i
C.A.B. Oliveira,i A. Ortiz de Solórzano,b,g J. Pérez,n J.L. Pérez Aparicio,o J. Renner,i
L. Ripoll, p A. Rodríguez,b,g J. Rodríguez,a F.P. Santos,e J.M.F. dos Santos,e
L. Segui,b,g L. Serra,a D. Shuman,i A. Simón,a C. Sofka,q M. Sorel,a J.F. Toledo,h
J. Torrent, p Z. Tsamalaidze,r J.F.C.A. Veloso,i J.A. Villar,b,g R.C. Webb,q J.T. White,q
N. Yahlalia
–1–
A BSTRACT: The “Neutrino Experiment with a Xenon Time-Projection Chamber” (NEXT) is intended to investigate the neutrinoless double beta decay of 136 Xe, which requires a severe suppression of potential backgrounds; therefore, an extensive screening and selection process is underway to control the radiopurity levels of the materials to be used in the experimental set-up of
NEXT. The detector design combines the measurement of the topological signature of the event for
background discrimination with the energy resolution optimization. Separate energy and tracking
readout planes are based on different sensors: photomultiplier tubes for calorimetry and silicon
multi-pixel photon counters for tracking. The design of a radiopure tracking plane, in direct contact with the gas detector medium, was a challenge since the needed components have typically
activities too large for experiments requiring ultra-low background conditions. Here, the radiopurity assessment of tracking readout components based on gamma-ray spectroscopy using ultra-low
background germanium detectors at the Laboratorio Subterráneo de Canfranc (Spain) is described.
According to the obtained results, radiopure enough printed circuit boards made of kapton and
copper and silicon photomultipliers, fulfilling the requirements of an overall background level in
that region of at most 8 × 10−4 counts keV−1 kg−1 y−1 , have been identified.
K EYWORDS : Double beta decay; Time-Projection Chamber (TPC); Gamma detectors (HPGe);
Search for radioactive material.
∗ Corresponding
† Spokesperson
author ([email protected]).
([email protected]).
Testing GeV-Scale Dark Matter with Fixed-Target Missing Momentum Experiments
Eder Izaguirre, Gordan Krnjaic, Philip Schuster, and Natalia Toro
Perimeter Institute for Theoretical Physics, Waterloo, Ontario, Canada
We describe an approach to detect dark matter and other invisible particles with mass below
a GeV, exploiting missing energy-momentum measurements and other kinematic features of fixedtarget production. In the case of an invisibly decaying MeV–GeV-scale dark photon, this approach
can improve on present constraints by 2–6 orders of magnitude over the entire mass range, reaching
sensitivity as low as 2 ∼ 10−14 . Moreover, the approach can explore essentially all of the viable
parameter space for thermal or asymmetric dark matter annihilating through the vector portal.
arXiv:1411.1404v1 [hep-ph] 5 Nov 2014
I.
INTRODUCTION
Existing techniques to search for dark matter (DM)
are most effective in two regimes: if dark matter is heavy
like a WIMP [1–7], or if it is very light and coherent like
an axion field [8–13]. If dark matter is lighter than a few
GeV and not coherent, then direct detection techniques
are notoriously difficult. But some of the most appealing
dark matter scenarios overlap with this difficult category,
such as the case when dark matter and baryons have a
common origin with comparable number densities [14, 15]
or DM is part of a hidden sector (see [16] for a review).
This largely open field of GeV-scale dark matter possibilities offers well-motivated discovery opportunities and
is ripe for experimental exploration.
In either of the above scenarios, DM must interact with
the Standard Model (SM) to avoid overproduction in the
early universe. Among the simplest such interactions are
those mediated by a kinetically mixed gauge boson (A0 )
associated with a dark sector gauge symmetry [25, 26].
Light DM that primarily annihilates through an off-shell
A0 into Standard Model particles is largely unconstrained
by available data [16]. With light DM and mediator mass
scales m comparable, an acceptably small relic density
robustly bounds the dark sector coupling αD and kinetic
mixing (see Sec. 2) by
−10
2
(αD 2 )relic density >
∼ O(1) × 10 (100 MeV/m) (1)
This is an important benchmark level of sensitivity to
reach to decisively probe this broad and widely considered framework for light DM.
Recently, new beam-dump experiments have aimed to
produce light DM candidates and then observe their scattering in downstream detectors [20, 27–35]. This is a
compelling technique to discover light DM, but its reliance on a small re-scattering probability prevents this
approach from reaching the milestone sensitivity of Eq. 1.
Achieving this sensitivity requires the identification of
DM production events based solely on their kinematics,
which in fixed-target electron-nuclear collisions is quite
distinctive [36]. Light DM candidates produced in such
collisions carry most of the incident beam-energy, so a
forward detector that can efficiently capture the energy of
electron/hadron showers can be used to observe this signature above irreducible backgrounds (which are small)
and reducible backgrounds (which require aggressive rejection). In fact, an effort to exploit this feature and
search for light DM using a secondary beam of electrons
from SPS spills at CERN was proposed in [17].
Our goals in this paper are twofold. We first evaluate the ultimate limitations for fixed-target DM searches
using missing energy-momentum. While neutrino production reactions set an in-principle background floor,
in practice such an experiment will likely be limited by
instrumental backgrounds — specifically, detection inefficiencies that allow rare photo-production reactions to
mimic the missing energy-momentum signature. This
conclusion motivates experimental scenarios that can
more efficiently reject such backgrounds. We therefore propose an experimental setup optimized to measure the recoil electron’s kinematics and demonstrate
that this measurement allows significantly improved kinematic background rejection and in situ measurements of
detector inefficiencies. This approach can reach the milestone sensitivity (1) to robustly test vector portal light
DM over the entire mass range from MeV−GeV. Moreover, a new-physics interpretation of any positive signal
would be greatly bolstered by these additional kinematic
handles.
Figure 1 summarizes the potential sensitivity for a few
benchmark scenarios, including for the first time in the
literature a realistic calculation of the DM signal yields.
Belle-II could explore the remaining m >GeV portion of
this target if mono-photon triggers are implemented [18].
Beyond dark matter physics, the approach we advocate
will play an important role in improving sensitivity to kinetically mixed dark photons that decay invisibly, nicely
complementing the ongoing program of searches for visible decays [29, 30, 37–55]. Indeed, while the window
identified six years ago for visibly decaying dark photons
to explain the muon g − 2 anomaly has recently been
closed [56], the corresponding parameter space for invisibly decaying dark-photons has not been fully explored.
The approach outlined in this paper will cover the entire g − 2 anomaly region for invisible decays (as does the
proposal of [17]) and has sensitivity that extends beyond
any existing or planned experiment by several orders of
magnitude, in a manner largely insensitive to model details.
Section II summarize our benchmark model for light
dark matter interacting with the standard model through
arXiv:1410.8386v1 [hep-ph] 30 Oct 2014
QCD and nuclear physics. How to explain the
coincidence between the radius of the strong
interaction of nucleons and the characteristic
scale of neutron-neutron electrostatic
interaction?
A.A. Godizov∗
Institute for High Energy Physics, 142281 Protvino, Russia
Abstract
An attempt is made to interpret, in the framework of QCD, the coincidence of two
observable scales which characterize the interaction between neutrons.
1. Introduction
The discovery of vector meson J/ψ in 1974 and the explanation of its decay width narrowness
in the framework of perturbative quantum chromodynamics (QCD) [1] induced a drastic rise of
interest to this quantum-field model from the scientific community, and, for more than 30 years,
QCD is the only world-wide recognized candidate for the position of the fundamental theory of
strong interaction. At present, a variety of very effective theoretical approximations exists: the
QCD sum rules, chiral perturbation theory, relativistic mean field theory, the Skyrme model,
lattice QCD, nonrelativistic models with “realistic” potentials, contact interaction models, bag
models etc. However, in spite of the impressive successes in development of these approaches,
many important problems related to putting QCD into agreement with experiment have not
been solved yet.
In this eprint an attempt is made to get within QCD an answer to the question from the
title (just for curiosity). At this, we will indispensably touch upon the problem of accordance
between the global color structure of chromodynamics and the dynamics of low-energy nuclear
systems.
2. Comparison of the two characteristic scales
The available experimental data on the neutron charge form factor allow, in principle, a straight
model-independent estimation of the characteristic scale of the electrostatic interaction between
neutrons, but, for simplicity, we use some test parametrization.
The electric charge distribution in nucleon can be represented as the superposition of two
functions which determine the distributions of the quarks u and d. Let us set the charge density
∗
1
Proton-induced cross-sections of nuclear reactions on lead up to 37 MeV
F. Ditróia,∗, F. Tárkányia , S. Takácsa , A. Hermanneb
a Institute
for Nuclear Research, Hungarian Academy of Sciences (ATOMKI), Debrecen, Hungary
b Cyclotron Laboratory, Vrije Universiteit Brussel (VUB), Brussels, Belgium
arXiv:1411.1901v1 [nucl-ex] 7 Nov 2014
Abstract
Excitation function of proton induced nuclear reactions on lead for production of 206,205,204,203,202,201g Bi,
203cum,202m,201cum
Pb and 202cum,201cum,200cum,199cum Tl radionuclides were measured up to 36 MeV by using activation
method, stacked foil irradiation technique and ?-ray spectrometry. The new experimental data were compared with
the few earlier experimental results and with the predictions of the EMPIRE 3.1, ALICE-IPPE (MENDL2p) and
TALYS (TENDL-2012) theoretical reaction codes.
Keywords: lead target, cross-section by proton activation, theoretical model codes, thin layer activation (TLA)
1. Introduction
Production cross-sections of proton induced nuclear
reactions on lead are important for many applications
and for the development of nuclear reaction theory.
Lead is an important technological material as pure element as well as alloying agent and it is also widely
used in different nuclear technologies, as well as target material for production of 201 Tl medical diagnostic
gamma-emitter for SPECT technology (Lagunas-Solar
et al., 1981). 205 Bi and 206 Bi have also medical interest,
while they are used to study biokinetics of medically interesting 212,213 Bi alpha-emitter radioisotopes (Milenic
et al., 2001). Lead and lead-bismuth alloy (Broome,
1996) are considered as target material for spallation
neutron sources, it is also used for Pb or Pb-Bi, PbMg cooled fast nuclear reactors and lead cooled accelerator driven reactors (IAEA, 2002). The beam handling and target systems (collimator, energy degrader,
target backing) are frequently made from lead (brass).
At charged particle accelerators, widely used different
alloys are also containing lead. In most of these applications high intensity, low and high energy direct or
secondary proton beams activate these technological elements and produce highly active radio-products. Recognizing the importance of knowledge of the production
cross-sections on a large energy scale systematic coordinated experimental and theoretical studies were indicated and large scale experiments were done. In spite of
∗ Corresponding
author: [email protected]
Preprint submitted to Applied Radiation and Isotopes
this, only a few experimental data sets exist, collected
mostly by the experimental groups. In the low energy
region practically only one experimental cross-section
is available from the Hannover-Cologne group. In our
research and application work in connection with the
activation cross-sections on lead we were involved in
different projects and applications:
• preparation of nuclear database for production of
medical radioisotopes in the frame of an IAEA Coordinated Research Project (Gul et al., 2001; Zaitseva et al., 1987), using the nat Pb(p,x)201 Tl reaction
• Preparation of proton and deuteron activation
cross-section database for FENDL Fusion Evaluated Data Library (IAEA, 2004)
• Investigating the activation cross-sections of
deuteron induced reactions on lead (Ditrói et al.,
2008)
• Preparation of data base of Thin Layer Activation
(TLA) technique for wear measurement (IAEANDS, 2010) via the nat Pb(p,x)206 Bi reaction
• Every day practice of wear measurement of brass
samples (Laguzzi et al., 2009)
The importance of the cross-section data for nuclear
databases was justified in preparation phase in practice
by selecting important targets for the database. From
other side, in our practice the importance of crosssection data is well known for choosing the appropriate
November 10, 2014

Proposal for a Detector of Photons with Zero Projection of... I. G. Savenko

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