Top Physics in WHIZARD

Transcription

Top Physics in WHIZARD
(+ NLO/QCD Status)
Jürgen R. Reuter, DESY
J.R.Reuter
Top Physics in WHIZARD (+NLO/QCD)
LCWS 2015, Whistler, 4.11.15
WHIZARD @
WHISTLER
J.R.Reuter
My tribute to Canada …
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✦
J.R.Reuter
in memoriam ✦
✦
in memoriam ✦
Jon Vickers, 29.10.1926 - 10.7.2015
J.R.Reuter
“Vergeh’ die Welt
meiner jauchzenden Eil’!
Die Leuchte verlischt, zu ihr!
Isolde!”
WHIZARD: Overview
WHIZARD v2.2.7
(11.08.2015)
http://whizard.hepforge.org
<[email protected]>
WHIZARD Team: Wolfgang Kilian,Thorsten Ohl, JRR
Simon Braß/Bijan Chokoufé/Marco Sekulla/Christian Weiss/Soyoung Shim/Florian Staub/Zhijie Zhao + 2 Master
(some losses: C. Speckner [software engineering], F. Bach [European Commission], S. Schmidt [Philosophy])
Publication: EPJ C71 (2011) 1742 (and others for O’Mega, Interfaces, color flow formalism)
J.R.Reuter
WHIZARD: Overview
WHIZARD v2.2.7
(11.08.2015)
http://whizard.hepforge.org
<[email protected]>
WHIZARD Team: Wolfgang Kilian,Thorsten Ohl, JRR
Simon Braß/Bijan Chokoufé/Marco Sekulla/Christian Weiss/Soyoung Shim/Florian Staub/Zhijie Zhao + 2 Master
(some losses: C. Speckner [software engineering], F. Bach [European Commission], S. Schmidt [Philosophy])
Publication: EPJ C71 (2011) 1742 (and others for O’Mega, Interfaces, color flow formalism)
LHC
2nd WHIZARD Workshop Würzburg, 03/2015
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K. Desch, DESY Th-WS ‘15
WHIZARD Parton Shower
Two independent implementations: kT-ordered QCD and Analytic QCD shower
Analytic shower: no shower veto exact shower history known, allows reweighting
Kilian/JRR/Schmidt/Wiesler, JHEP 1204 013 (2012)
Technical overhaul of the shower / merging part
Plans: implement GKS matching, QED shower (also interleaved, infrastructure ready)
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Tuning of the WHIZARD Parton Shower
First tunes of both kT-ordered QCD and Analytic QCD shower Chokoufe/Englert/JRR,
Di- and Multijet data from LEP as given in RIVET analysis
Usage of the PROFESSOR tool for determining the best fit Buckley et al., 2009
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2015
NLO Development in WHIZARD
Need for precision predictions that match (sub-) percent experimental accuracy
mainly NLO corrections, but also QED and electroweak (ee)
Binoth Les Houches Interface (BLHA): Workflow
1. Process definition in SINDARIN (contract to One-Loop Program [OLP])
2. OLP generates code (Born/virtual interference), WHIZARD reads contract
3. NLO matrix element library loaded into WHIZARD
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Working NLO interfaces to:
(first focus on QCD corrections)
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GoSam
[G. Cullen et al.]
OpenLoops [F. Cascioli et al.]
GoSam
[G. Cullen et al.]
WHIZARD v2.2.6 contains alpha version
QCD corrections (massless and massive emitters)
alpha_power = 2
alphas_power = 0
process eett = e1,E1 => t, tbar
{ nlo_calculation = “full” }
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GoSam
[G. Cullen et al.]
alpha_power = 2
alphas_power = 0
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GoSam
[G. Cullen et al.]
fixedorder
1000
800
[fb]
600
alpha_power = 2
alphas_power = 0
400
200
onshell, LO
onshell, NLO
offshell, LO
offshell, NLO
0
350
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400
450
p
500
550
600
s [GeV]
FKS Subtraction
(Frixione/Kunszt/Signer)
Subtraction formalism to make real and virtual contributions separately finite
d
NLO
=
Z
|
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d
n+1
R
{z
finite
d
S
+
}
Z
|
d
n+1
S
+
{z
finite
Z
d
n
V
}
FKS Subtraction
d
NLO
=
Z
|
d
n+1
R
d
S
{z
+
}
finite
✴
Z
|
d
n+1
S
+
{z
Z
d
n
finite
V
}
Automated subtraction terms in WHIZARD,
algorithm:
Find all singular pairs
I = {(1, 5), (1, 6), (2, 5), (2, 6), (5, 6)}
✴
Partition phase space according to singular regions
1=
X
S↵ ( )
↵2I
✴
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Generate subtraction terms for singular regions
FKS Subtraction
d
NLO
=
Z
|
d
n+1
R
d
S
{z
+
}
finite
✴
Z
|
d
n+1
S
+
{z
Z
d
n
finite
V
}
Automated subtraction terms in WHIZARD,
algorithm:
Find all singular pairs
I = {(1, 5), (1, 6), (2, 5), (2, 6), (5, 6)}
✴
Partition phase space according to singular regions
1=
X
S↵ ( )
↵2I
✴
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Generate subtraction terms for singular regions
Examples and Validation
Simplest benchmark process:
e+ e ! q q̄
with
NLO
LO
/
LO
= ↵s /⇡
Plot for total cross section for fixed
strong coupling constant
List of validated QCD NLO processes
•
e+ e ! q q̄
•
e+ e ! q q̄g
•
e+ e ! `+ ` q q̄
• Cross-checks with MG5_aMC@NLO
•
e+ e ! `+ ⌫` q q̄
• Phase space integration for virtuals performs great
•
e+ e ! tt̄
•
e+ e ! tW b
•
e+ e ! W + W bb̄
•
e+ e ! tt̄H
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Examples and Validation
Simplest benchmark process:
e+ e ! q q̄
with
NLO
LO
/
LO
= ↵s /⇡
Plot for total cross section for fixed
strong coupling constant
List of validated QCD NLO processes
•
e+ e ! q q̄
•
e+ e ! q q̄g
•
e+ e ! `+ ` q q̄
• Cross-checks with MG5_aMC@NLO
•
e+ e ! `+ ⌫` q q̄
• Phase space integration for virtuals performs great
•
e+ e ! tt̄
•
e+ e ! tW b
✦
QCD NLO infrastructure in pp complete
•
e+ e ! W + W bb̄
✦
•
e+ e ! tt̄H
First attempts on electroweak corrections,
interfacing the RECOLA code [Denner et al.]
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NLO Fixed-Order Events
Add weights of real emission events to weight of Born kinematics using the FKS mapping
Output weighted events in WHIZARD (e.g. using HepMC), then analysis with Rivet
Example process: e+ e ! W + W bb̄
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Completed: polarized NLO results (remember: ILC will always run with polarization)
Produce also plots including complete ISR photon radiation and beamstrahlung
NLO decays also available (Initial state Jacobian, important for consistent widths)
Investigate the full 2 ➝ 6 process: e+e- ➝ bbeμνν
[Chokoufé/Kilian/Lindert/JRR/Pozzorini/Weiss]
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Automated POWHEG Matching in WHIZARD
Soft gluon emissions before hard emission generate large logs
1
kTmax
2
Perturbative αs : |Msoft | ⇠ k2 ! log kmin
T
T
Consistent matching of NLO matrix element with shower
POWHEG method: hardest emission first [Nason et al.]
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1
kTmax
2
T
T
• Complete NLO events
B(
n)
= B(
n)
+V(
n)
• POWHEG generate events according to the formula:
d = B(
n)

NLO min
(kT )
R
• Uses the modified Sudakov form factor:
 Z
NLO
(kT ) = exp
d
R
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+
+
Z
d
rad R(
R(
NLO
(kT )
R
R( n+1 )
✓(kT (
rad
B( n )
n+1 )
n+1 )
B(
n)
n+1 )
d
rad
kT )
1
kTmax
2
T
T
• Complete NLO events
B(
n)
= B(
n)
+V(
n)
• POWHEG generate events according to the formula:
d = B(
n)

NLO min
(kT )
R
• Uses the modified Sudakov form factor:
 Z
NLO
(kT ) = exp
d
R
+
+
Z
d
rad R(
R(
NLO
(kT )
R
R( n+1 )
✓(kT (
rad
B( n )
n+1 )
n+1 )
B(
n)
n+1 )
d
rad
kT )
Hardest emission: kTmax ; shower with imposing a veto
B < 0 if virtual and real terms larger than Born: shouldn’t happen in perturbative regions
Reweighting such that B > 0 for all events
POWHEG: Positive Weight Hardest Emission Generator own implementation in WHIZARD
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POWHEG Matching, example: e+e- to dijets
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Examples: Top pairs and tth production
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Top Threshold at lepton colliders
ILC top threshold scan best-known method to measure top quark mass, ΔΜ ~ 30-50 MeV
Heavy quark production at lepton colliders, qualitatively:
Threshold region: top velocity v ~ αs ⪡ 1
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⌫=
rp
s
2mt + i
m
t
Top Threshold Resummation in (p)NRQCD
NRQCD is EFT for non-relativistic quark-antiquark systems: separate M·v and M·v 2
Integrate out hard quark and gluon d.o.f.
Resummation of singular terms close to threshold (v = 0) Hoang et al. ’99-‘01; Beneke et al., ’13-‘14
Phase space of two massive particles
R⌘
tt̄
µµ
=v
X ⇣ ↵ s ⌘k X
k
v
i
i
(↵s ln v) ⇥
⇥ 1 (LL); ↵s , v (NLL); ↵s2 , ↵s v, v 2 (NNLL)
(p/v)NRQCD EFT w/ RG improvement
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R⌘
tt̄
=v
µµ
X ⇣ ↵ s ⌘k X
k
v
i
i
(↵s ln v) ⇥
R
,Z
v
v
a
a
(s) = F (s)R (s) + F (s)R (s)
|
{z
}
|
{z
}
s-wave: LL+NLL
p-wave⇠v 2 :NNLL
but contributes
at NLL differentially!
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R⌘
tt̄
=v
µµ
X ⇣ ↵ s ⌘k X
k
v
i
i
(↵s ln v) ⇥
R
,Z
v
v
a
a
(s) = F (s)R (s) + F (s)R (s)
|
{z
}
|
{z
}
s-wave: LL+NLL
p-wave⇠v 2 :NNLL
but contributes
Coulomb potential gluon ladder resumption
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R⌘
tt̄
=v
µµ
X ⇣ ↵ s ⌘k X
k
v
i
i
(↵s ln v) ⇥
R
,Z
v
v
a
|
a
(s) = F (s)R (s) + F (s)R (s)
|
{z
}
|
{z
}
s-wave: LL+NLL
{z
}
can be mapped onto effective ttV vertex
p-wave⇠v 2 :NNLL
but contributes
Coulomb potential gluon ladder resumption
far away from
threshold
C3
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v/a
G(N)LL
=
v/a
pole p
G(N)LL (↵s , Mt , s, |~
pt | ,
t)
differential in off-shell tt phase space
Top Threshold in WHIZARD
with F. Bach/B. Chokoufe/A. Hoang/M. Stahlhofen/C. Weiss
Implement resummed threshold effects as effective vertex [form factor] in WHIZARD
Gv,a (0, pt , E + i t , ⌫) from TOPPIK code [Jezabek/Teubner], included in WHIZARD
Default parameters:
M 1S = 172 GeV,
M 1S = Mtpole (1
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NLO
t
= 1.409 GeV
↵s (MZ ) = 0.118
LL/N LL
(Coul.) )
[P. Marquard’s talk]
Default parameters:
M 1S = 172 GeV,
M 1S = Mtpole (1
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NLO
t
= 1.409 GeV
↵s (MZ ) = 0.118
LL/N LL
(Coul.) )
Default parameters:
M 1S = 172 GeV,
NLO
t
= 1.409 GeV
↵s (MZ ) = 0.118
LL/N LL
(Coul.) )
M 1S = Mtpole (1
Theory uncertainties from scale variations:
hard and soft scale
µh = h · mt
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µ s = f · mt v
Sanity checks: correct limit for αs ⟶ 0, stable against variation of cutoff ΔM [15-30 GeV]
Why include LL/NLL in a Monte Carlo event generator?
Important effects: beamstrahlung; ISR; LO electroweak terms
More exclusive observables accessible
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Forward-backward asymmetry
(norm. good shape stability)
Af b :=
(ptz > 0)
(ptz ) < 0)
(ptz > 0) + (ptz < 0)
Matching to continuum at LO and NLO
analytic+whizard-onshell
1000
800
600
[fb]
• Transition region between relativistic and
resummation effects
• CLIC benchmark energies:
0.38 TeV, 1.4 TeV, 3.0 TeV
• Remove double-counting NLO / (N)LL
400
200
onshell, NLO
expanded FF, onshell, mpole = m1S
expanded FF, onshell, mpole = m1S , nopwave
AnalyticOneloop, mpole = m1S , onshell
0
340
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350
360
p
370
s [GeV]
380
390
400
resummation effects
0.38 TeV, 1.4 TeV, 3.0 TeV
1000
1000
onshell, NLO
800
800
[fb]
[fb]
600
600
400
400
Resummed formfactor, expanded to O(↵s )
rp
s 2mt + i t
⌫=
p = |~
p|
p0 = E t
m
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200
200
mt
onshell, NLO
00
344.0
340
350 344.5 360
345.0
p 370
s [GeV]
380 345.5 390
346.0
400
resummation effects
0.38 TeV, 1.4 TeV, 3.0 TeV
1000
1000
onshell, NLO
800
800
[fb]
[fb]
600
600
400
400
rp
s 2mt + i t
⌫=
p = |~
p|
p0 = E t
m
200
200
mt
onshell, NLO
00
344.0
340
350 344.5 360
345.0
p 370
s [GeV]
380 345.5 390
346.0
400
Matching formula
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resummation effects
0.38 TeV, 1.4 TeV, 3.0 TeV
1000
1000
onshell, NLO
800
800
[fb]
[fb]
600
600
400
400
rp
s 2mt + i t
⌫=
p = |~
p|
p0 = E t
m
200
200
mt
Matching formula
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onshell, NLO
00
344.0
340
350 344.5 360
345.0
p 370
s [GeV]
380 345.5 390
346.0
400
Switch-off function
Threshold-continuum matching
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Conclusions & Outlook
WHIZARD 2.2 event generator for collider physics (ee, pp, ep)
Focus here on top physics at ee colliders
(QCD) NLO automation: reals and subtraction terms (FKS) [+
virtuals externally] ➝ WHIZARD 3.0
Automated POWHEG matching (other schemes in progress)
Polarized results and decays available at NLO (QCD)
Top threshold in e+e-: NLL NRQCD threshold / NLO
continuum matching
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continuum matching
Future projects: inclusion of tth threshold
Long term: QED/EW NLO, QED Shower, NNLO QCD
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continuum matching
Experimentalists present !?!?
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continuum matching
Experimentalists present !?!?
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Time for the:
Experimentalists’ ILC/CLIC NLO Wishlist
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Top Physics in WHIZARD

Transcription

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