Using hot quarks to examine the quark-gluon-plasma

Transcription

Using particle correlations to probe
the medium produced at RHIC
Helen Caines - Yale University
Oxford/RAL
November 2008
Relativistic Heavy-Ion Collider (RHIC)
PHOBOS
PHENIX
1 km
RHIC
BRAHMS
STAR
v = 0.99995⋅c
AGS
Au+Au @ √sNN=200 GeV
TANDEMS
Helen Caines - Yale - Nov 2008 - Oxford/RAL
2
QGP expectation came from Lattice
ε/T4 ~ # degrees of freedom
deconfined:
many d.o.f.
confined:
few d.o.f.
3
QGP expectation came from Lattice
ε/T4 ~ # degrees of freedom
deconfined:
many d.o.f.
confined:
few d.o.f.
TC ≈ 173 MeV ≈ 2⋅1012 K
εC ≈ 0.7 GeV/fm3 (~6x normal nuclear densities)
3
RHIC has created a new state of matter
The QGP is the:
hottest (T=200-400 MeV ~ 2.5 1012 K)
densest (ε = 30-60 εnuclear matter)
matter ever studied in the lab.
It flows as a
(nearly) perfect fluid
with systematic patterns, consistent with
quark degree of freedom
and a viscosity to entropy density ratio
lower
than any other known fluid.
4
RHIC has created a new state of matter
The QGP is the:
hottest (T=200-400 MeV ~ 2.5 1012 K)
densest (ε = 30-60 εnuclear matter)
matter ever studied in the lab.
It flows as a
(nearly) perfect fluid
with systematic patterns, consistent with
quark degree of freedom
and a viscosity to entropy density ratio
lower
than any other known fluid.
Want to learn more about the properties
4
Elliptic flow – rapid thermalization
e
n
la
10
!
nP
tio
c
ea
5
y (fm)
R
m
a
e
Initial spatial anisotropy
A Fourier expansion used
to describe the angular
distribution of the particles
"R
0
!5
b
b
!-"R
!10
Interactions
Au+Au at b=7 fm
!10
!5
0
5
10
x (fm)
Final momentum anisotropy
dN
dϕ
∝ 1 + 2v2 cos[2(ϕ − ψR )] + ...
5
e
n
la
10
!
nP
tio
c
ea
5
y (fm)
R
m
a
e
!10
"R
0
!5
b
b
!-"R
Interactions
Au+Au at b=7 fm
!10
!5
0
5
10
x (fm)
dN
dϕ
∝ 1 + 2v2 cos[2(ϕ − ψR )] + ...
Driving spatial anisotropy vanishes ⇒ self quenching
5
e
n
la
10
!
nP
tio
c
ea
5
y (fm)
R
m
a
e
!-"R
"R
0
!5
b
b
!10
Interactions
Au+Au at b=7 fm
!10
!5
0
5
10
x (fm)
dN
dϕ
∝ 1 + 2v2 cos[2(ϕ − ψR )] + ...
Driving spatial anisotropy vanishes ⇒ self quenching
Sensitive to early interactions and pressure gradients
5
The flow is ~Perfect
Huge asymmetry found at RHIC
2v2
• massive effect in azimuthal
distribution w.r.t reaction
plane
• At higher pT: Factor 3:1 peak
to valley from 25% v2
6
The flow is ~Perfect
Huge asymmetry found at RHIC
2v2
• massive effect in azimuthal
distribution w.r.t reaction
plane
• At higher pT: Factor 3:1 peak
to valley from 25% v2
“fine structure” v2(pT)
• ordering with mass of
particle
• good agreement with
ideal hydrodynamics
(zero viscosity, λ=0)
“perfect liquid”
6
The constituents “flow”
mT =
!
p2T + m20
baryons
mesons
7
baryons
mesons
• Scaling flow parameters by quark content nq (baryons=3,
mesons=2) resolves meson-baryon separation of final state hadrons
7
baryons
mesons
• Scaling flow parameters by quark content nq (baryons=3,
mesons=2) resolves meson-baryon separation of final state hadrons
Constituents of liquid are partons
7
How perfect is “Perfect” ?
Viscous fluid
• supports a shear stress
• viscosity η:
η
≈ momentum density × mean free path
1
p̄
≈ np̄λ = np̄
=
nσ
σ
Fx
∂vx
= −η
A
∂y
• small η ⇒ large σ ⇒ strong couplings
8
How perfect is “Perfect” ?
Viscous fluid
• supports a shear stress
• viscosity η:
η
≈ momentum density × mean free path
1
p̄
≈ np̄λ = np̄
=
nσ
σ
Fx
∂vx
= −η
A
∂y
• small η ⇒ large σ ⇒ strong couplings
Hydrodynamic calculations for RHIC assumed zero viscosity
η = 0 ⇒ “perfect fluid”
• But there is a (conjectured) quantum limit:
‣ derived first in (P. Kovtun, D.T. Son, A.O. Starinets, PRL.94:111601, 2005)
motivated by AdS/CFT correspondence
N.B.: water (at normal conditions) η/s ~ 380 ћ/4π
8
What is η/s at RHIC ?
conjectured quantum limit
4
H 2O
3
N2
!/s
He
2
Meso
1
nG
as
Observables that are sensitive to shear
•
•
•
0
-1.0
-0.5
0.0
Elliptic Flow
(T-T0)/T0
‣ R. Lacey et al.: Phys. Rev. Lett. 98:092301, 2007
‣ H.-J. Drescher et al.: Phys. Rev. C76:024905, 2007
pT Fluctuations
‣ S. Gavin and M. Abdel-Aziz: Phys. Rev. Lett. 97:162302, 2006
Heavy quark motion (drag, flow)
‣ A. Adare et al. : Phys. Rev. Lett. 98:092301, 2007
P
QG
RHIC
0.5
1.0
9
Probing the medium - Jet production
Early production in parton-parton scatterings with large Q2.
Direct interaction with partonic phases of the reaction
From p+p
 Obtain jet rate
 Obtain fragmentation functions
Schematic view of jet production
hadrons
leading
particle
q
q
leading
particle
hadrons
10
From p+p
 Obtain jet rate
In A+A look at
 attenuation or absorption of jets:
“jet quenching”
 suppression of high p hadrons
T


jet production in quark matter
hadrons
leading
particle
q
q
modification of angular correlation
changes of particle composition
10
From p+p
 Obtain jet rate
In A+A look at
 attenuation or absorption of jets:
“jet quenching”
 suppression of high p hadrons
T


modification of angular correlation
changes of particle composition
jet production in quark matter
hadrons
leading
particle
q
q
Differences due to medium
10
Jets – a calibrated probe?
STAR : PRL 97 (2006) 252001
Jet production in p+p understood in pQCD framework
11
Jets – a calibrated probe?
PHENIX
STAR : PRL 97 (2006) 252001
K.Reygers QM2008
STAR : PLB 637 (2006) 161
S. Albino et al, NPB 725 (2005) 181
Jet production in p+p understood in pQCD framework
Particle production in p+p also well modeled.
Seems we have a reasonably calibrated probe
11
Charged hadron ξ in p+p 200 GeV
20<Ereco<30 GeV
30<Ereco<40 GeV
40<Ereco<50 GeV
R<0.4
M. Heinz
Hard Probes 2008
Reasonable agreement between Pythia and data
12
Charged hadron ξ in p+p 200 GeV
20<Ereco<30 GeV
30<Ereco<40 GeV
40<Ereco<50 GeV
R<0.4
M. Heinz
Hard Probes 2008
Reasonable agreement between Pythia and data
R<0.7
Are these differences onset of beyond LL effects?
12
ξ for strange hadrons
10<Ereco<15
pT<0.5
15<Ereco<20
20<Ereco<50
R<0.4
R<0.5
R<0.7
M. Heinz Hard Probes 2008
Clear differences between particles
13
Back to probing the medium
Compare Au+Au with p+p Collisions
Nuclear
Modification
Factor:
RAA
Average number
of NN collision
in an AA collision
No “Effect”:
R < 1 at small momenta
R = 1 at higher momenta where
hard processes dominate
Suppression: R < 1
14
High-pT suppression
Observations at RHIC:
1. Photons are not suppressed

figure by D.

Good! γ don’t interact with
medium
Ncoll scaling works
15
High-pT suppression

figure by D.

medium
Ncoll scaling works
2. Hadrons are suppressed in
central collisions

Huge: factor 5
15
High-pT suppression

figure by D.

medium
Ncoll scaling works
2. Hadrons are suppressed in
central collisions

Huge: factor 5
3. Hadrons are not suppressed
in peripheral collisions

Good! medium not dense
15
Interpretation
Gluon radiation: Multiple finalstate gluon radiation off the
produced hard parton induced
by the traversed dense colored
medium
!=xE
E
Hard
Production
!=(1-x)E
"qT~µ
!
"
Medium
16
Interpretation
!=xE
Gluon radiation: Multiple finalstate gluon radiation off the
produced hard parton induced
by the traversed dense colored
medium
•
sQGP
10. 0
q (GeV2/fm)
E
Hard
Production
QGP
1. 0
!=(1-x)E
"qT~µ
!
"
Medium
Mean parton energy loss ∝ medium
properties:
‣ ΔEloss ~ ρgluon (gluon density)
‣ Coherence among radiated gluons
‣ ΔEloss ~ ΔL2 (medium length)
⇒ ~ ΔL with expansion
•
0. 1
Hadronic Matter
is 〈kT2〉 transferred per unit path length
cold nuclear matter
0. 01
0. 1
q̂ = q̂(!r, τ )
R. Baier, Nucl. Phys. A715, 209c
1
10
! (GeV/fm3)
Characterization of medium
‣ transport coefficient
100
‣ gluon density dNg/dy
16
The model landscape (not exhaustive)
PQM (Parton Quench model)
Implementation of BDMPS (calc. E
loss via coherent gluon radiation many soft scattering approx.
Realistic geometry
Static medium, q time average (i.e.
depends on initial density, scheme
evolution dependent )
No initial state multiple scatterings
No modified PDFs
WHDG
Implementation of GLV formalism (calc.
E loss via gluon brehmsstralung -few
hard scatterings) + collisional energy
loss.
Realistic geometry - integral over all
paths
Expanding medium
No initial state multiple scatterings
GLV
Implementation of GLV formalism
(calc. E loss via gluon
brehmsstralung -few hard
scatterings.)
Realistic geometry
Bjorken expanding medium - Calc.
a priori (w/o E loss) average path
length - use to calc. partonic E loss
ZOWW
Modified fragmentation model
(radiative gluon E loss
incorporated into effective medium
modified FF)
Hard sphere geometry
Expanding medium
17
Constraining q^
Model
PQM: A. Dainese, C. Loizides, G. Paic, Eur. Phys. J C38: 461
Opacity Parameter
(2005). C. Loizides, Eur. Phys. J.C49, 339 (2007).
PQM
〈q〉 = 13.2 (+ 2.1 - 3.2)
GLV: I. Vitev, Phys. Lett. B639, 38 (2006). M. Gyulassy, P.
GLV
dNg/dy = 1400 (+270 -150)
WHDG: W.A. Horowitz, S. Wicks, M. Djordjevic, M.
WHDG
dNg/dy = 1400 (+200 -375)
ZOWW ε0 = 1.9 (+0.2 - 0.5)
Levai, I. Vitev, Nucl. Phys. B571, 197 (2000).
preparation; S. Wicks, W. Horowitz, M. Djordjevic,
(〈q〉~7)Gyulassy,in
M. Gyulassy, Nucl. Phys. A 783, 493 (2007); S. Wicks, W.
(〈q〉~1)
Horowitz, M. Djordjevic,M. Gyulassy, Nucl. Phys. A 784, 426
(2007).
ZOWW: H. Zhang, J.F. Owens, E. Wang, X-N Wang, Phys
Rev. Lett. 98: 212301 (2007).
PHENIX: http://arxiv.org/abs/0801.1665
WHDG
PQM
〈q〉 only the
natural unit
in PQM
GLV
Need other observables
to dis-entangle all the
possible effects
ZOWW
18
Jet correlations in heavy-ion collisions
• Full jet reconstruction very challenging
background from bulk similar to signal for jet pT<~30 GeV
p+p collisions
Au+Au collisions
19
Jet correlations in heavy-ion collisions
• Full jet reconstruction very challenging
background from bulk similar to signal for jet pT<~30 GeV
p+p collisions
Au+Au collisions
Use di-hadron correlations
r
trigge
pT asso Δφ
pT
Trigger
c
Back-to-back
φtrigger (near side)
(away side)
jet
jet
19
RHIC seminal di-hadron results
“The disappearance of the
away-side jet”
4 < pTtrig < 6 GeV/c
pTassoc>2 GeV/c
d+Au results similar to p+p
→ final state interaction
→ d+Au can be used as the
reference measurement instead of
p+p
Phys Rev Lett 90, 082302
20
RHIC seminal di-hadron results
“The disappearance of the
away-side jet”
pTassoc>2 GeV/c
d+Au results similar to p+p
→ final state interaction
→ d+Au can be used as the
reference measurement instead of
p+p
→ yield reduced compared
to d+Au
1/Ntrig dN/d(Δφ)
“High pT Punch-through”
Away side correlation reappears
for high pT correlations
Phys Rev Lett 90, 082302
d+Au
Au+Au 20-40%
pTassoc>6 GeV/c
Au+Au 0-5%
STAR PRL 97 (2006) 162301
20
Away-side di-hadron fragmentation
• Study medium-induced
modification of fragmentation
function due to energy loss
• Without full jet reconstruction,
parton energy not measurable
• z not measured (z=phadron/
pparton )
• zT=pT,assoc/pT,trig
21
H. Zhong et al., PRL 97 (2006) 252001
C. Loizides, Eur. Phys. J. C 49, 339-345 (2007)
• Study medium-induced
6< pT trig < 10 GeV
1
IAA
Au-Au
Cu-Cu
Au-Au modified frag
Cu-Cu modified frag
Au-Au PQM q=4
Cu-Cu PQM q=3
Au-Au PQM q=7
Cu-Cu PQM q=5.5
Au-Au PQM q=14
Cu-Cu PQM q=9
-1
10 0
50
O. Catu QM2008
100
150
200
250
300
modification of fragmentation
function due to energy loss
• Without full jet reconstruction,
parton energy not measurable
• z not measured (z=phadron/
pparton )
350
• zT=pT,assoc/pT,trig
Npart
Inconsistent with Parton
Quenching Model calculation
better
21
1/Ntrig dN/dzT
H. Zhong et al., PRL 97 (2006) 252001
C. Loizides, Eur. Phys. J. C 49, 339-345 (2007)
6< pT trig < 10 GeV
IAA
Au-Au
Cu-Cu
Au-Au modified frag
Cu-Cu modified frag
Au-Au PQM q=4
Cu-Cu PQM q=3
Au-Au PQM q=7
Cu-Cu PQM q=5.5
Au-Au PQM q=14
Cu-Cu PQM q=9
10-10
50
O. Catu QM2008
100
ratio to d-Au
1
p+p theory
Cu+Cu 0-10% theory
Cu+Cu 40-60% theory
1
10-1
d-Au
Cu-Cu 0-10%
Au-Au 30-40%
Cu-Cu 40-60%
Au-Au 60-80%
Au-Au 0-12%
Npart = 100
Npart = 20
10-2
2
STAR Preliminary
1
150
200
250
300
Npart
Inconsistent with Parton
Quenching Model calculation
better
350
0
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
zT=passoc
/ptrig
T
T
Denser medium in central Au+Au
than central Cu+Cu
Similar medium for similar Npart
Vacuum fragmentation after
parton Eloss in the medium
21
Two particles are better than one
Compare fits to RAA and IAA
H. Zhang, J.F. Owens, E. Wang, X.N. Wang
Phys. Rev. Lett. 98: 212301 (2007)
χ2(IAA)
• Minima of data in same place
• Sharper for di-hadrons
χ2(RAA)
^
q0τ0 ~ q=2.8
±0.3 GeV2/fm
22
Two particles are better than one
Compare fits to RAA and IAA
H. Zhang, J.F. Owens, E. Wang, X.N. Wang
Phys. Rev. Lett. 98: 212301 (2007)
χ2(IAA)
• Minima of data in same place
• Sharper for di-hadrons
χ2(RAA)
^
q0τ0 ~ q=2.8
±0.3 GeV2/fm
Parton production points in transverse plane
Single Hadrons
di-Hadrons
• Surface bias effectively
leads to saturation of
RAA with density
minimize bias:
di-hadron correlations
full jets
Renk and Eskola, hep-ph/0610059
22
Path length dependencies
Non-central events have “elliptic” overlap geometries
Measurements w.r.t reaction plane angle:
Change path length
Keep everything else same
Isolate effects due to path length
23
Path length effect on di-hadron correlation
in-plane φt-ΨRP=0
B. Cole QM2008
out-of-plane φt-ΨRP=90o
– Near side peak unchanged
– Shoulder peaks emerge as φt - Ψ increases but are at fixed Δφ
– Head peak (di-jet remnant) decreases as φt - ΨRP increases
24
Centrality and path length effects
Au+Au 200 GeV
STAR Preliminary
0-5%
20-60%
v2 sys. error
v2{RP}
v2{4}
A. Feng QM2008
3< pTtrig <
RMS
4 GeV/c, 1.0 < pTasso < 1.5 GeV/c
In-plane:
20-60% ~ d+Au
0-5% > d+Au
Out-of-plane: 20-60% ~ 0-5%
Au+Au > d+Au
25
Centrality and path length effects
Au+Au 200 GeV
STAR Preliminary
0-5%
20-60%
v2 sys. error
v2{RP}
v2{4}
A. Feng QM2008
3< pTtrig <
RMS
4 GeV/c, 1.0 < pTasso < 1.5 GeV/c
In-plane:
20-60% ~ d+Au
0-5% > d+Au
Out-of-plane: 20-60% ~ 0-5%
Away-side features reveal
path length effects
Au+Au > d+Au
25
Deflected jets or conical emission?
near
STAR Preliminary
Medium
away
Deflected jets
near
Medium
Conical emission or deflected
jets?
Distinguish between models
using 3-particle correlations
away
Conical Emission
26
near
STAR Preliminary
Medium
away
Deflected jets
Deflected jets
near
Medium
Conical Emission
Conical emission or deflected
jets?
Distinguish between models
using 3-particle correlations
away
Conical Emission
26
near
STAR Preliminary
away
Deflected jets
Deflected jets
near
d+Au
3 < pTtrig < 4 GeV/c, 1 < pTassoc< 2 GeV/c
Medium
Medium
Conical Emission
away
Conical Emission
Au+Au 0-12%
26
STAR Preliminary
Deflected jets
(Δφ1-Δφ2)/2
d+Au
Au+Au 0-12%
Conical Emission
(Δφ1-Δφ2)/2
d+Au
Au+Au 0-12%
26
STAR Preliminary
Deflected jets
d+Au
(Δφ1-Δφ2)/2
d+Au
Au+Au 0-12%
Conical Emission
(Δφ1-Δφ2)/2
Au+Au data
consistent with
Conical
emission
Au+Au 0-12%
26
Possible causes of conical emission
Mach Cone
Similar to jet
creating
sonic boom
in air.
Energy radiated from parton
deposited in collective
hydrodynamic modes.
•Mach angle depends on Cs
• T dependent
• Angle independent of pTassoc
27
Possible causes of conical emission
Mach Cone
Čerenkov Gluon Radiation
Similar to jet
creating
sonic boom
in air.
Energy radiated from parton
deposited in collective
hydrodynamic modes.
•Mach angle depends on Cs
Gluons radiated by
superluminal parton.
cn
v parton
= cos(θ c )
c
=
n( p)v parton
• T dependent
1
≈
n( p)
Angle dependent on pTassoc
• Angle independent of pTassoc
€
27
Mach cone or Čerenkov gluons?
Angle predictions:
• Mach-cone:
Čerenkov gluon radiation:
Angle decreases with
associated pT
Au+Au 0-12%
(Δφ1-Δφ2)/2
Cone angle (radians)
Angle independent of associated pT
STAR Preliminary
J. Ulery QM2006
pT (GeV/c)
28
Angle predictions:
• Mach-cone:
associated pT
Au+Au 0-12%
(Δφ1-Δφ2)/2
PHENIX
1D analysis
M. McCumber QM2008
STAR Preliminary
J. Ulery QM2006
pT (GeV/c)
28
Angle predictions:
• Mach-cone:
✓
✗
associated pT
Au+Au 0-12%
(Δφ1-Δφ2)/2
PHENIX
1D analysis
M. McCumber QM2008
STAR Preliminary
J. Ulery QM2006
pT (GeV/c)
28
Parton interactions on near side
Δ(φ) correlations
29
Δ(φ) correlations
Δ(η) − Δ(φ) correlations
Long range Δ(η) correlation
– the “Ridge”
29
Δ(φ) correlations
Δ(η) − Δ(φ) correlations
Long range Δ(η) correlation
– the “Ridge”
Persists out to very large Δ(η) >2
29
Energy loss of trigger -“The ridge”
d+Au, 40-100%
Au+Au, 0-5%
3 < pT(trig) < 6 GeV
2 < pT(assoc) < pT(trig)
30
d+Au, 40-100%
Au+Au, 0-5%
C. Nattrass QM2008
Ridge: Increases with Npart
Independent of colliding system
30
d+Au, 40-100%
Au+Au, 0-5%
C. Nattrass QM2008
Jet: Approx. flat with Npart
30
d+Au, 40-100%
Au+Au, 0-5%
C. Nattrass QM2008
Jet: Approx. flat with Npart
Parton interacts with medium (ridge), then vacuum fragments (jet)?
30
Spectra of ridge and shoulder particles
Preliminary
Ridge
Jet
J. Putschke QM2006
sloperidge > slopejet
~ slopeinclusive
31
Spectra of ridge and shoulder particles
Preliminary
Ridge
Jet
J. Putschke QM2006
sloperidge > slopejet
~ slopeinclusive
≥ slopeshoulder
M. McCumber QM2008
31
Un-triggered pair correlations
Method: measure pair densities ρ(η1-η2,φ1-φ2) for all possible pairs in same and
mixed events.
Define correlation measure as:
M. Daugherty QM2008
Minijet:
Same-side jet-like
correlations with no
trigger particle
32
STAR Preliminary
Helen
Caines - Yale
- Nov 2008 - Oxford/RAL
M. Daugherty
QM2008
33
Small residual indicates goodness of fit
Helen
Caines - Yale
- Nov 2008 - Oxford/RAL
M. Daugherty
QM2008
34
Evolution of mini-jet with centrality
Same-side
peak
83-94%
ary
elimin
Pr
STAR
55-65%
STAR
inary
Prelim
46-55%
Pr
STAR
ary
elimin
0-5%
Prelim
STAR
inary
idth
ηΔ w
Little shape change from
peripheral to 55% centrality
Large change
within ~10%
centrality
Smaller change from transition
to most central
M. Daugherty QM2008
35
Same-side
peak
83-94%
55-65%
ary
elimin
Pr
STAR
STAR
inary
Prelim
46-55%
Pr
STAR
ary
elimin
0-5%
Prelim
STAR
inary
idth
ηΔ w
Large change
within ~10%
centrality
peripheral to 55% centrality
peak amplitude
peak η width
STAR Preliminary
STAR Preliminary
Smaller change from transition
to most central
200 GeV
62 GeV
binary scaling
references
ν
path length ν
M. Daugherty QM2008
35
Same-side
peak
83-94%
ary
elimin
Pr
STAR
55-65%
STAR
inary
Prelim
46-55%
ary
elimin
Pr
STAR
0-5%
Prelim
STAR
inary
idth
ηΔ w
Large change
Binary scaling reference followed until
sharp transition atSmaller
ρ ~ 2.5change from transition
within ~10%
to mostcorrelation
central
~30% of
the hadrons
participate in the same-side
peripheral
to 55%
centrality in central Au+Aucentrality
peak amplitude
peak η width
peak amplitude
STAR Preliminary
STAR Preliminary
peak η width
STAR Preliminary
STAR Preliminary
200 GeV
62 GeV
binary scaling
references
200 GeV
62 GeV
ν
path length ν
Transverse particle density
M. Daugherty QM2008
35
Jets @ RHIC in Au-Au collisions
~ 47 GeV
STAR preliminary
pt per grid cell [GeV]
Clearly visible in central
events on E-by-E basis
η
ϕ
J. Putschke Hard Probes 2008
36
Jets @ RHIC in Au-Au collisions
~ 47 GeV
STAR preliminary
Clearly visible in central
events on E-by-E basis
~ 21 GeV
η
ϕ
STAR preliminary
Energies as low as
20 GeV resolvable
η
ϕ
36
Jet-finding strategies in heavy-ion
Jet energy fraction outside cone
R=0.3
CDF preliminary
• Unmodified (p+p) jets:
~ 80% of energy within R~0.3
• Need to suppress heavy-ion background:
R=
Δη 2 + Δφ 2
small jet cones areas
R~0.3-0.4
remove underlying event
pt,track ,Et,tower >1-2 GeV
€
37
Jet-finding strategies in heavy-ion
Jet energy fraction outside cone
R=0.3
CDF preliminary
• Unmodified (p+p) jets:
~ 80% of energy within R~0.3
• Need to suppress heavy-ion background:
R=
€
Estimate
Δη 2 + Δφ 2
small jet cones areas
R~0.3-0.4
remove underlying event
pt,track ,Et,tower >1-2 GeV
background E-by-E by sampling Out-of-Cone area:
STAR preliminary
Out-of-Cone area:
used to estimate mean background
energy and “mean background FF
function”
Caveat: Precision depends on acceptance, event-byevent fluctuations and elliptic flow (small effect for
central heavy-ion collisions) …
η
ϕ
reconstructed jets
37
Jet spectrum in Au+Au collisions
STAR preliminary; stat. errors only
HT not trigger bias corrected!
LOCone
Rc=0.4, ptSeed>4.6 GeV
ptcut>1 GeV
MB-Trig: Good agreement with
Nbin scaled p+p collisions
HT-Trig: Large trigger bias how far
up does it persist? (in p+p at least to
30 GeV)
Relative normalization systematic
uncertainty: ~50%.
Au+Au HT 0-10%
Au+Au MB 0-10%
p+p scaled by Nbin
Further statistics of MB is needed
to assess the bias in HT Trigger.
black points: p+p mid-cone corrected to particle level (scaled by Nbin)
blue solid points: Au+Au minbias corrected for ptcut and eff. using Pythia
red open points: Au+Au HT trigger not corrected for ptcut and eff. using
Pythia
First reconstructed
jets in central heavy
ion collisions.
S. Salur Hard Probes 2008
38
Modification of fragmentation function
• MLLA: good description of vacuum fragmentation (basis of PYTHIA)
• Introduce medium effects at parton splitting Borghini and Wiedemann, hep-ph/0506218
Jet quenching
“hump-back
plateau”
pThadron~2 GeV
ξ=ln(EJet/phadron)
Jet quenching
fragmentation should be strongly modified at pThadron~1-5 GeV
Can we measure this at RHIC?
39
RHIC “Summary”
We create a strongly coupled medium ⇒ sQGP
•
•
not the asymptotically plasma of “free” quarks and gluons as expected - high pT
partons interact very strongly with it
It flows like a (nearly) perfect fluid with quark degrees of freedom and a
viscosity to entropy density ratio lower than any other known fluid
We are past the discovery stage ⇒ towards the quantitative
•
•
•
•
•
i.e. η/s, transport coefficients
First full jet reconstruction in heavy-ion collisions - probing medium
How medium varies as a function of collision energy/centrality/species
New phenomena (e.g. ridge) challenge our understanding
much remains to be done: EOS, initial conditions (ultimately needs EIC)
Next steps
•
•
•
Ongoing upgrades to STAR and PHENIX
‣ Vertex detectors, increased coverage and PID, improved triggering
capabilities ⇒ rare probes, heavy flavor, γ-jet, ...
Electron Beam Ion Source (EBIS) to extend ranges of species (U+U)
RHIC-II: increase luminosity by factor 5 using stochastic cooling
40
The Next Energy Frontier: LHC
A unique opportunity to investigate “QGP” at unparalleled high √s
Will this too create a
strongly-coupled fluid?
16
!SB/T4
RHIC
14
3 flavor
!/T4
12
2+1 flavor
10
2 flavor
8
LHC
SPS
6
4
0 flavor
2
0
100
200
300
400
500
600
T (MeV)
Targeted Studies: ATLAS
Targeted Studies: CMS
Dedicated Experiment: ALICE
41

Using hot quarks to examine the quark-gluon-plasma

Transcription

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