Production of a photon in association with a heavy quark ... · Production of a photon in...
Transcript of Production of a photon in association with a heavy quark ... · Production of a photon in...
Production of a photon in association with a heavy quark jet in pA and AA
collisions
I. SchienbeinLPSC Grenoble/Univ. Grenoble
9th International Workshop on High-pT Physics at LHCLPSC Grenoble, 24 - 28 September 2013
EAOM LPSC, Serge Kox, 20/9/2012
CampusUniversitaire
Laboratoire de Physique Subatomique et de Cosmologie
Monday, October 8, 12
Saturday, September 28, 13
Introduction
Saturday, September 28, 13
γ+Q production is a versatile process!
• in pp collisions:
• probe of heavy quark PDFs
• intrinsic charm (IC)/ intrinsic bottom (IB)
• in pA collisions:
• probe of nuclear PDFs (gluon, heavy quarks)
• in AA collisions:
• probe of heavy quark energy loss
Saturday, September 28, 13
γ+Q production at NLODirect Photon and Heavy Quarks - hardscattering
how are they produced?
Leading Order - O(↵↵s
) - Only one hard-scattering subprocess
Compton Subprocess g + Q ! Q + �
Next-to-Leading Order - O(↵↵2
s
)
Real Corrections - 2 ! 3 body scattering subprocesses
g + g ! Q + Q̄ + � Q + Q ! Q + Q + �g + Q ! g + Q + � Q + Q̄ ! Q + Q̄ + �Q + q ! q + Q + � q + q̄ ! Q + Q̄ + �Q + q̄ ! Q + q̄ + �
Virtual Corrections - interference between LO Born diagram andvirtual diagrams
T. Stavreva Probing IC through � + Q production
[T. Stavreva, J. Owens, PRD79(2009)054017]
Saturday, September 28, 13
Fragmentation contributionDirect Photon and Heavy Quarks - fragmentation
LO: include all 2 ! 2 subprocesses ⇠ O(↵2
s
),O(↵2
s
)⌦ D�/q,g ⇠ ↵2
s
↵/↵s
= ↵↵s
Q
Q̄
Q
Q̄
Also need to include NLO fragmentation contributions - convoluteall 2 ! 3 ⇠ O(↵3
s
) with � FF
Q
Q̄
Reduced due to isolation requirements
minimizes background from photons : ⇡0 ! ��
T. Stavreva Probing IC through � + Q production
Saturday, September 28, 13
Final state collinear singularity in qq̄ ! QQ̄+ �Final State Collinear Singularity: qq̄ ! QQ̄�
q
q̄
Q
Q̄
1)
q
q̄
Q
Q̄
2)
Unlike for inclusive direct photon the annihilation subprocess doesnot appear at LO
q
q̄
Jet observed in final state (not meson ! no HQ FF)
Regulate singularity by retaining HQ mass: (pQ
+ p
¯
Q
)2 > 4m2
Q
T. Stavreva Probing IC through � + Q productionSaturday, September 28, 13
γ+Q in pp collisions
References:T. Stavreva, J. Owens, PRD79(2009)054017Bednyakov, Demichev, Lykasov, Stavreva, Stockton,arXiv:1305.3548
Saturday, September 28, 13
Is there charm in the nucleon?
• Standard approach: Charm entirely perturbative
• Heavy Flavour Schemes
• FFNS: charm not in the protonkeep logs(Q/m) in fixed order
• VFNS: charm PDF in the protonresum logs(Q/m)
• Different Heavy Flavour Schemes = different ways to organize the perturbation series
• What is structure? What is interaction?Freedom to choose the factorization scale
• However, charm not so much heavier than Lambda_QCD
• There could be a non-perturbative intrinsic charm component
• Important to test the charm PDF experimentally
LO NLO N2LO N3LO
Full ACOT
ACOT Extension to Higher Orders 29
Based on the Collins-Wilczek-Zee (CWZ) Renormalization Scheme… hence, extensible to all orders
DGLAP kernels & PDF evolution are pure MS-BarSubtractions are MS-Bar
ACOT: mÆ 0 limit yields MS-Bar
with no finite renormalization
LO NLO N2LO N3LO
Full ACOT
ACOT Extension to Higher Orders 29
Based on the Collins-Wilczek-Zee (CWZ) Renormalization Scheme… hence, extensible to all orders
DGLAP kernels & PDF evolution are pure MS-BarSubtractions are MS-Bar
ACOT: mÆ 0 limit yields MS-Bar
with no finite renormalizationSaturday, September 28, 13
How to Access Heavy Flavor Components Directly??? 23
c g→ c γb g→ b γ
s g→ c W
c g→ b W
How to access the heavy quark PDFs directly?
Saturday, September 28, 13
How to Access Heavy Flavor Components Directly??? 23
c g→ c γb g→ b γ
s g→ c W
c g→ b W
How to access the heavy quark PDFs directly?
Saturday, September 28, 13
Results from TevatronComparison between theory & data
Measurements by DØ Collaboration [arXiv:0901.0739]
0 50 100 150 200
pTγ(GeV)
0.0001
0.001
0.01
0.1
1
dσ/d
p Tγ(p
b/G
eV)
yγyQ>0
0 50 100 150 200
yγyQ<0
p+p -> γ+b+X √$S = 1.96 TeV
0 50 100 150 200
pTγ(GeV)0.0001
0.001
0.01
0.1
1
10
dσ/d
p Tγ(p
b/G
eV)
yγyQ>0
0 50 100 150 200
yγyQ<0
p+p -> γ+c+X √$S = 1.96 TeV
Really good agreement for � + b
Not so for � + c
Given this: Possible explanation - existence of intrinsic charm ratherthan higher order corrections
T. Stavreva Probing IC through � + Q production
Saturday, September 28, 13
Intrinsic Charm effect on γ+c
Intrinsic Charm e↵ect on � + c
50 100 150pTγ
0
0.5
1
1.5
2
2.5
3
3.5
Data/Theory
µ=pTγµ=0.5pTγµ=2pTγBHPSSea-like
yγyQ>0
50 100 150pTγ
0
0.5
1
1.5
2
2.5
3
3.5
Data/Theory
µ=pTγµ=0.5pTγµ=2pTγBHPSSea-like
yγyQ<0
Sealike - overshoots data at low pT and undershoots at high pT
BHPS - the cross section grows at large pT, but still below dataResult inconclusive -
New Measurements - Tevatron - CDF & DØTest at pp Colliders - RHIC & LHC
T. Stavreva Probing IC through � + Q production
•BHPS IC: cross section grows at large pT but still below data
•Results inconclusive:•new measurements at Tevatron: CDF & D0• test at pp colliders: RHIC & LHC
Saturday, September 28, 13
New results from D0
new results DØ
(GeV)!
Tp
0 50 100 150 200 250 300
Ra
tio
to
NL
O
-1
0
1
2
3
4
5
6
Data / NLOSHERPA / NLOPYTHIA / NLO
fact./ NLOTk
Scale uncertaintyPDF uncertainty
Sea-like IC/CTEQBHPS IC/CTEQ
-1DØ, L = 8.7 fb
|<1.0!
|y
>15 GeVjet
T|<1.5, p
jet|y
(GeV)!
Tp
0 50 100 150 200 250 300
(p
b/G
eV
)! T
/dp
" d
-410
-310
-210
-110
1
| < 1.0!
data, |y
| < 2.5!
data, 1.5 < |y
NLO (Stavreva, Owens) fact. (Lipatov, Zotov)Tk
SHERPA, v1.3.1
PYTHIA, v6.420
>15 GeVjet
T|<1.5, p
jet|y
(x0.3)
-1DØ, L = 8.7 fb
� + c - left - arXiv:1210.5033� + b - right - arXiv:1203.5865Even higher discrepancy - now consider all leading jets
T. Stavreva Probing IC through � + Q production
Even larger discrepancy now!
Saturday, September 28, 13
• Tevatron: q-qbar channel
• effectively LO
• dominant at pT > 70 GeV
• large NNLO corrections!?
• LHC:
• g & Q initiated subprocesses dominate (>80%)
• expect no anomaly
• important to measure, probe of IC
• For many more details (predictions for RHIC, LHC, used cuts, γ+b, etc.) see:
• Talk T. Stavreva at DIS 2013
• arXiv:1305.3548
Discussion: Is there a QCD anomaly?Subprocess Contributions
50 100 150 200pTγ(GeV)
1e-08
1e-06
0.0001
0.01
1
dσ/d
p Tγ(p
b/G
eV)
NLOqq->QQγqQ->qQγgQ->gQγLO+gg->QQγQQ->QQγ
p+p -> γ+b+X√$ S =1.96 TeV
At pT� ⇠ 70 GeV qq̄ ! QQ̄� starts to dominate
Abundance of q & q̄ at pp̄ colliders
T. Stavreva Probing IC through � + Q production
Subprocess Contributions in pp Collisions
50 100 150
pTγ(GeV)0.1
1
10
100
1000
10000
dσ/d
p Tγ(p
b/G
eV) NLO
LO+gg->QQγgQ->gQγqq->QQγqQ->qQγ ; QQ->QQγ
p+Pb-> γ +c +X √$ S = 8800 GeV, nCTEQ
g & Q initiated subprocesses dominate ( > 80% ) ) sensitivity togluon and HQ PDFs.
T. Stavreva Probing IC through � + Q production
Saturday, September 28, 13
• Tevatron: q-qbar channel
• effectively LO
• dominant at pT > 70 GeV
• large NNLO corrections!?
• LHC:
• g & Q initiated subprocesses dominate (>80%)
• expect no anomaly
• important to measure, probe of IC
• For many more details (predictions for RHIC, LHC, used cuts, γ+b, etc.) see:
• Talk T. Stavreva at DIS 2013
• arXiv:1305.3548
Discussion: Is there a QCD anomaly?Subprocess Contributions
50 100 150 200pTγ(GeV)
1e-08
1e-06
0.0001
0.01
1
dσ/d
p Tγ(p
b/G
eV)
NLOqq->QQγqQ->qQγgQ->gQγLO+gg->QQγQQ->QQγ
p+p -> γ+b+X√$ S =1.96 TeV
At pT� ⇠ 70 GeV qq̄ ! QQ̄� starts to dominate
Abundance of q & q̄ at pp̄ colliders
T. Stavreva Probing IC through � + Q production
Subprocess Contributions in pp Collisions
50 100 150
pTγ(GeV)0.1
1
10
100
1000
10000
dσ/d
p Tγ(p
b/G
eV) NLO
LO+gg->QQγgQ->gQγqq->QQγqQ->qQγ ; QQ->QQγ
p+Pb-> γ +c +X √$ S = 8800 GeV, nCTEQ
g & Q initiated subprocesses dominate ( > 80% ) ) sensitivity togluon and HQ PDFs.
T. Stavreva Probing IC through � + Q production
Saturday, September 28, 13
• Tevatron: q-qbar channel
• effectively LO
• dominant at pT > 70 GeV
• large NNLO corrections!?
• LHC:
• g & Q initiated subprocesses dominate (>80%)
• expect no anomaly
• important to measure, probe of IC
• For many more details (predictions for RHIC, LHC, used cuts, γ+b, etc.) see:
• Talk T. Stavreva at DIS 2013
• arXiv:1305.3548
Discussion: Is there a QCD anomaly?Subprocess Contributions
50 100 150 200pTγ(GeV)
1e-08
1e-06
0.0001
0.01
1
dσ/d
p Tγ(p
b/G
eV)
NLOqq->QQγqQ->qQγgQ->gQγLO+gg->QQγQQ->QQγ
p+p -> γ+b+X√$ S =1.96 TeV
At pT� ⇠ 70 GeV qq̄ ! QQ̄� starts to dominate
Abundance of q & q̄ at pp̄ colliders
T. Stavreva Probing IC through � + Q production
Subprocess Contributions in pp Collisions
50 100 150
pTγ(GeV)0.1
1
10
100
1000
10000
dσ/d
p Tγ(p
b/G
eV) NLO
LO+gg->QQγgQ->gQγqq->QQγqQ->qQγ ; QQ->QQγ
p+Pb-> γ +c +X √$ S = 8800 GeV, nCTEQ
g & Q initiated subprocesses dominate ( > 80% ) ) sensitivity togluon and HQ PDFs.
T. Stavreva Probing IC through � + Q production
Saturday, September 28, 13
γ+Q in pA collisions
References:T. Stavreva et al., JHEP1101(2011)152
Saturday, September 28, 13
Nuclear PDFs: needed for pA collisionsGlobal fits
Global fit analyses of nuclear parton densities
DIS and Drell-Yan data [ EKS98, HKM, nDS, nDSg, nCTEQ ]
. . . and hadron production at RHIC [ EPS09, DSSZ ]
QuestionHow to probe small-x gluon shadowing at LHC ?
which observables
why prompt photons look promising
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 4 / 25
Global fits
Global fit analyses of nuclear parton densities
DIS and Drell-Yan data [ EKS98, HKM, nDS, nDSg, nCTEQ ]
. . . and hadron production at RHIC [ EPS09, DSSZ ]
0.20.40.60.81.01.21.4
10-4 10-3 10-2 10-1 1
EPS09NLOnDSHKN07
G(,
2 =1.69GeV
2 )Pb
[ EPS09 Eskola, Paukkunen, Salgado 0902.4154 ]
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 4 / 25
gluongluon nCTEQ decut3gx fits nCTEQ decut3gx fits
x
A=1,2,4,9,12,27,56,108,207
● This still underestimates the true uncertainty
● Some curves lie outside the error bands of EPS'09 and/or HKN'07!
Friday, April 6, 12
[EPS09, Eskola, Paukkunen, Salgado, 0902.4154] [nCTEQ, 0907.2357 & 1012.1178]
Saturday, September 28, 13
nCTEQ PDFs with uncertainties
13
nCTEQ nCTEQ nuclear correction factors
with uncertainties
different solution for d-valence & u-valence
compared to EPS09
larger uncertainty @ gluon nuclear correction
factor & bigger low-x suppression
sea quark nuclear correction factors similar to
EPS09
Ri(Pb) =f
Pbi (x,Q)
f
pi (x,Q)
Q2 = 100 GeV2Pb
PREL
IMINA
RY
Q2 = 100 GeV2@
nuclear correction factors depend largely on
underlying proton baseline
13
nCTEQ nCTEQ nuclear correction factors
with uncertainties
different solution for d-valence & u-valence
compared to EPS09
larger uncertainty @ gluon nuclear correction
factor & bigger low-x suppression
sea quark nuclear correction factors similar to
EPS09
Ri(Pb) =f
Pbi (x,Q)
f
pi (x,Q)
Q2 = 100 GeV2Pb
PREL
IMINA
RY
Q2 = 100 GeV2@
nuclear correction factors depend largely on
underlying proton baseline Q2=100 GeV2
Pb
Preliminary
work in progress, see [K. Kovarik et al, 1307.3454]
Saturday, September 28, 13
• Jets
• Tevatron incl. jet data already used
• Prompt Photons
• Arleo et al, JHEP1104(2011)055
• d’Enterria, Rojo, NPB860(2012)311
• Virtual Photons
• see talk by M. Klasen
• Photons + Heavy Quarks
• T. Stavreva et al., JHEP1101(2011)152 (this talk)
• Open heavy quarks?
• Heavy Quarkonia?
How to probe the gluon distribution?
Kinematical range
1
10
10 2
10 3
10 4
10 5
10 6
10 -6 10 -5 10 -4 10 -3 10 -2 10 -1
photons
heavy bosonsjets
NMCQs
2
x
Q2 (G
eV2 )
(x ,Q2) domain covered at the LHC
Photons and jets are clearly complementary
Photons cover small Q2 where shadowing should be large
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 6 / 25
LHC kinematics
Saturday, September 28, 13
• Jets
• Tevatron incl. jet data already used
• Prompt Photons
• Arleo et al, JHEP1104(2011)055
• d’Enterria, Rojo, NPB860(2012)311
• Virtual Photons
• see talk by M. Klasen
• Photons + Heavy Quarks
• T. Stavreva et al., JHEP1101(2011)152 (this talk)
• Open heavy quarks?
• Heavy Quarkonia?
How to probe the gluon distribution?
Kinematical range
1
10
10 2
10 3
10 4
10 5
10 6
10 -6 10 -5 10 -4 10 -3 10 -2 10 -1
photons
heavy bosonsjets
NMCQs
2
x
Q2 (G
eV2 )
(x ,Q2) domain covered at the LHC
Photons and jets are clearly complementary
Photons cover small Q2 where shadowing should be large
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 6 / 25
LHC kinematics
Saturday, September 28, 13
Predictions in p A collisions
NLO calculations assuming that charm PDF is radiatively generated(c(x , µ = mc) = 0)
dc(x ,Q)
dt=
!s
2"
!
dy
y[c(x/y)PQ!Q(y) + g(x/y)Pg!Q (y)]
in the variable flavour number scheme
Probing charm nPDF allows for constraining the gluon sector
0
0.5
1
1.5
2
RgPb
nCTEQEPS09HKN07
0
0.5
1
1.5
RcPb
0.001 0.01 0.1x0
0.5
1
1.5
Ru v
Pb
u
0
0.5
1
1.5
2
RcPb/RgPb
nCTEQEPS09HKN07
0.01 0.1x0
0.5
1
1.5
RcPb/Ru v
Pb
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 18 / 25
Predictions in pA
Saturday, September 28, 13
Predictions in p A collisions
NLO calculations assuming that charm PDF is radiatively generated(c(x , µ = mc) = 0)
dc(x ,Q)
dt=
!s
2"
!
dy
y[c(x/y)PQ!Q(y) + g(x/y)Pg!Q (y)]
in the variable flavour number scheme
Predictions at RHIC and LHCRHIC: d Au collisions at
!sNN
= 200 GeVLHC: p Pb collisions at
!sNN
= 8.8 TeV
Calculation of quenching factors
R!QpA =
# (pA " $ Q X)
A # (pp " $ Q X)
using di!erent nPDF sets then available: nCTEQ, EPS09, HKN07
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 18 / 25
Predictions in pA
Saturday, September 28, 13
Spectra and rates
Absolute cross sections
10 15 20 25
pTγ(GeV)
1
10
100
1000
10000
dσ/d
p Tγ(p
b/G
eV) NLO
LO+gg->QQγgQ->gQγqq->QQγqQ->qQγ ; QQ->QQγ
d+Au-> γ +c +X √$ S = 200 GeV, nCTEQ
50 100 150
pTγ(GeV)0.1
1
10
100
1000
10000
dσ/d
p Tγ(p
b/G
eV) NLO
LO+gg->QQγgQ->gQγqq->QQγqQ->qQγ ; QQ->QQγ
p+Pb-> γ +c +X √$ S = 8800 GeV, nCTEQ
Cross section dominated by Compton scattering
Important NLO corrections
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 19 / 25
Spectra and rates
Saturday, September 28, 13
Spectra and rates
Expected rates at RHIC (PHENIX kinematics)
Assuming Lyear = 0.74 pb!1
Photon + charm
N ! 3" 104 for pT!> 7 GeV
N ! 102 for pT!> 20 GeV
Photon + bottom
< 100 events for pT!> 17 GeV
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 19 / 25
Spectra and rates
Saturday, September 28, 13
Spectra and rates
Expected rates at LHC (ALICE kinematics)
Assuming Lyear = 0.1 pb!1
!pPb!+Q NpPb
!+Q
" + c PHOS 22700 pb 2270" + b PHOS 3300 pb 330" + c EMCal 119000 pb 11900" + b EMCal 22700 pb 2270
Large for " + c and " + b events at LHC
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 19 / 25
Spectra and rates
Saturday, September 28, 13
Constraining the gluon nPDF
LHC
50 100
pTγ(GeV)0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
1.15
1.2
1.25
Rσγ+
c
EPS09HKN07nCTEQ
p+Pb->γ+c+X / p+p->γ+c+X √$ S = 8800GeV
0.01x0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
1.15
1.2
1.25
RgPb
EPS09HKN07nCTEQ
Nuclear Modifications for gp/Pb(x,Q=50 GeV)
R!+cpPb follows RPb
g very closely
Almost no overlap between EPS09 and HKN07, and nCTEQ decut3
Measurements with su!ciently small error bars should disentangle thevarious nPDF sets
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 20 / 25
Constraining the gluon nPDF
Main result
Saturday, September 28, 13
Constraining the gluon nPDF
RHIC
8 10 12 14 16 18 20
pTγ(GeV)0.8
1
1.2
1.4
1.6
1.8
RdA
uγ+c
nCTEQnCTEQ - no nuclear corrections to dEPS09HKN07
d+Au->γ+c+X / p+p->γ+c+X √# S = 200 GeV
0.1 x0.8
1
1.2
1.4
1.6
1.8
RgA
u
nCTEQEPS09HKN07
Nuclear Modifications for gp/Au(x, Q = x √#S / 2 ~ pT)
Same observation than at LHC : R!+cdAu ! RAu
g
Kinematic region probed at RHIC (x = 10!1–2" 10!1)complementary to that at LHC (x = 5" 10!3–2 " 10!2)
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 20 / 25
Constraining the gluon nPDF
Main result
Saturday, September 28, 13
Conclusions I
• g+Q initiated subprocesses dominate
• In standard approach: Heavy quark PDF dynamically generated; clean probe of gluon PDF
• No isospin effects! Quenching factor R=1 if no nuclear effects
• Cross sections large enough at RHIC and LHC
•
• Baseline for photon+Q production in AA collisions
Constraining the gluon nPDF
LHC
50 100
pTγ(GeV)0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
1.15
1.2
1.25
Rσγ+
c
EPS09HKN07nCTEQ
p+Pb->γ+c+X / p+p->γ+c+X √$ S = 8800GeV
0.01x0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
1.15
1.2
1.25
RgPb
EPS09HKN07nCTEQ
Nuclear Modifications for gp/Pb(x,Q=50 GeV)
R!+cpPb follows RPb
g very closely
Almost no overlap between EPS09 and HKN07, and nCTEQ decut3
Measurements with su!ciently small error bars should disentangle thevarious nPDF sets
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 20 / 25
Saturday, September 28, 13
γ+Q in AA collisions
References:T. Stavreva, F. Arleo, IS, JHEP1302(2013)072
Saturday, September 28, 13
Probing (massive) parton energy loss in QGP
Energy loss of massive partons
Heavy quark mass acts as a collinear cuto! for medium-induced gluonradiation, just like in vacuum (dead cone) [ Doskhitzer Kharzeev 2001 ]
Clear hierarchy expected!
"E"
"
g>#
"E"
"
q> "E
"
"
c> "E
"
"
b
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 21 / 25
Probing (massive) parton energy loss in QGP
Saturday, September 28, 13
Probing (massive) parton energy loss in QGP
Energy loss of massive partons
Heavy quark mass acts as a collinear cuto! for medium-induced gluonradiation, just like in vacuum (dead cone) [ Doskhitzer Kharzeev 2001 ]
Clear hierarchy expected!
"E"
"
g>#
"E"
"
q> "E
"
"
c> "E
"
"
b
[ ALICE ]
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 21 / 25
Probing (massive) parton energy loss in QGP
Saturday, September 28, 13
Probing (massive) parton energy loss in QGP
Energy loss of massive partons
Heavy quark mass acts as a collinear cuto! for medium-induced gluonradiation, just like in vacuum (dead cone) [ Doskhitzer Kharzeev 2001 ]
Clear hierarchy expected!
"E"
"
g>#
"E"
"
q> "E
"
"
c> "E
"
"
b
! + Q unique tool to probe Q energy loss in the plasma
γ γ c γ bq
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 21 / 25
Probing (massive) parton energy loss in QGP
Saturday, September 28, 13
Analysis in A A collisions
Calculations performed at NLO accuracy at!s = 5.5 TeV
Heavy quark energy loss !Qestimated on an event-by-event basis from
the quenching weight (probability distribution) obtained perturbatively[ Armesto Dainese Salgado Wiedemann 2005 ]
Various observables investigatedPhoton–jet energy asymmetry AJ
AJ =ET1 " ET2
ET1 + ET2,!" > #/2
Momentum imbalance z!Q
z!Q = "$pT! .$pTQp2T!
Photon–jet pair momentum q!
q! = |pT! + pTQ |Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 22 / 25
Analysis in AA collisions
Saturday, September 28, 13
Transverse momentum distributions
[ Stavreva FA Schienbein 2013 ]
Comparing photon and jet p! spectra
No (or little) modifications of the photon p!
Stronger e!ects on the heavy quark jet spectrum
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 23 / 25
Transverse momentum distributions
Saturday, September 28, 13
Transverse momentum distributions
[ Stavreva FA Schienbein 2013 ]
Nuclear production ratios RAA
Sensitive to the amount of energy loss assumed in the calculation
Needs to be compared to !+ inclusive jet production
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 23 / 25
Transverse momentum distributions
Saturday, September 28, 13
Pair momentum distribution
Why q! distribution
q! ! !Qat LO accuracy if the photon is produced directly
The shift in the q! distributions should reflect the strength of heavyquark energy loss in the medium
Francois Arleo (LLR & LAPTh) ! and !+Q production in p A collisions Trento Workshop pA@LHC 24 / 25
Pair momentum distribution
Saturday, September 28, 13
Conclusions II
• AA→γ+Q very interesting processAllows to study heavy quark energy loss in the QGP calibrated against the photon
• Performed first exploratory study at NLO for the LHC
Saturday, September 28, 13
Merci!
Saturday, September 28, 13
INTRINSIC CHARM
Intrinsic charm:c(x , µ0) 6= 0 at initial scale µ0 = mc
Models implemented in CTEQ 6.5C (PRD75, 2007)global fit allows average momentum hxic+c̄ or order 1 %
1 Light-cone Fock-space picture (Brodsky et al.), concentrated at large xhxic+c̄ = 0.57, 2.0 %
2 Meson-cloud model (Navarra et al.)hxic+c̄ = 0.96, 1.8 %
3 Phenomenological model: sea-like charm, broad in xhxic+c̄ = 1.1, 2.4 %
H. Spiesberger (Mainz) DIS, 27. 3. 2012 28 / 37
A colleague: “If QCD is right, there has to be IC”(which normalization?)
Intrinsic Charm
Recent CTEQ-TEA analysis of IC: 1309.0025
Saturday, September 28, 13
Results for LHC - ATLAS
LHC - ATLASExperimental Cuts
p
T
Rapidity Isolation Cuts
Photon p
min
T ,� = 45 GeV |y� | < 1.37 R = 0.4, ET
= 7 GeVp
max
T ,� = 1000 GeV 1.52 < |y� | < 2.37Heavy Jet p
min
T ,Q = 20 GeV |yQ
| < 2.4 R
jet
> 0.4,RQ� > 1
T. Stavreva Probing IC through � + Q production
� + c Central Rapidity
IC shows up at much higher pT
dependence on rapidity
T. Stavreva Probing IC through � + Q production
γ+c, central rapidity
Saturday, September 28, 13
Results for LHC - ATLAS
LHC - ATLASExperimental Cuts
p
T
Rapidity Isolation Cuts
Photon p
min
T ,� = 45 GeV |y� | < 1.37 R = 0.4, ET
= 7 GeVp
max
T ,� = 1000 GeV 1.52 < |y� | < 2.37Heavy Jet p
min
T ,Q = 20 GeV |yQ
| < 2.4 R
jet
> 0.4,RQ� > 1
T. Stavreva Probing IC through � + Q production
γ+c, forward rapidity
� + c Forward Rapidity
x ⇠ p
TpS
(ey1 + e
y
2)
Consider forward rapidities at LHC
T. Stavreva Probing IC through � + Q production
Saturday, September 28, 13
Results for RHIC - PHENIX
RHIC - PHENIXExperimental Cuts
p
T
Rapidity Isolation Cuts
Photon⇤ p
min
T ,� = 7 GeV |y� | < 0.35 R = 0.5, ✏ < 0.1E�
Heavy Jet p
min
T ,Q = 5 GeV |yQ
| < 0.8 ——
T. Stavreva Probing IC through � + Q production
Intrinsic Charm at RHIC
10 15 20 25pTγ(GeV)
0.01
0.1
1
10
100
dσ/d
p Tγ(p
b/G
eV)
NLOLOBHPSsea-like
pp-> γ +c +X √$ S = 200GeV, CTEQ6.6M
10 15 20 25pTγ
0
1
2
3
4
(dσBHPS;sea-like;LO/dp T
γ)/(dσCTEQ6.6M/dp T
γ)
BHPSsea-likeLO
Small center of mass energy probes high x ⇠ p
T
/pS
Cross section is very sensitive to IC - especially BHPS
T. Stavreva Probing IC through � + Q production
Saturday, September 28, 13