Punch-through Jets in A+A Collisions at RHIC/LHC
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Transcript of Punch-through Jets in A+A Collisions at RHIC/LHC
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Punch-through Jets in A+A Collisions at RHIC/LHC
Han-Zhong ZhangInstitute of Particle Physics, Huazhong Normal University, China
Collaborators: J. Owens, E. Wang and X.-N. Wang
Quark Matter 2008 Feb. 4-10 , 2008
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I. IntroductionII. Fragility of single/dihadron suppression factorsIII. Single/dihadron spectra at RHIC/LHCIV. Azimuthal angle anisotropy of single/dihadron
spectra at RHIC/LHCV. Conclusions
Outline
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I. Introduction
What happens for a jet propagating inside QGP?
Jet quenching:
The hard jet loses a significant amount of its energy
via radiating gluon induced by multiple scattering.
hadrons
q
q
hadrons
leadingparticle
leading particle
N-N collision
hadrons
q
q
hadrons
Leading particle suppressed
leading particle suppressed
A-A collision
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Jet Quenching effect in AA is incorporated via modified fragmentation functions.
FFstd
dPDFsT
dydp
dAB
T
AA
ˆ2
Nuclear geometry
A NLO pQCD parton model with jet quenching in A+A
Partondistribution
functions
NLO cross
sections
(X. -N. Wang , PRC70(2004)031901)),(
)],(/),()[1(),,(
2'0/
/
2'0/
'2'0
/
'/2
/
cchL
gghc
gcch
c
cLccch
zDe
zDz
zLzD
z
zeEzD
,//),/( ''cTgcTcTc EpLzEppz
Jet energy loss
5
Parton jet energy loss per unit length:
),(5.0
),/5.7/()6.1/( 02.1
01
partpartd
NsdN
dNEE
dL
dE
E. Wang , X. -N. Wang , PRL87(2001)142301)
B. B. Back for PHOBOS, nucl-ex/0604017v1
),(
),(
0
0
part
part
Nsf
Nsf
Initial gluon density coefficient
Energy loss parameter
),(5.0
),(
00
partpart
part NsdN
dNNsf
(a parameterization form of theory calculations)
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II. Fragility of single/dihadron suppression factors
Simultaneous fit of single/dihadron spectra
In most central Au+Au
dihadronsingle hadron
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2 -fit to both suppression factors
95.045.0
158
T
trigT
z
GeVp
GeVpT 204 for single
for dihadron
fmGeV /1.25.10 H. Zhang, J.F. Owens, E. Wang and
X.-N. Wang , PRL 98(2007)212301
Iaa robust when Raa fragile at RHIC
Sharp concave
Flat concave
in most central Au+Au
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Surviving jets: close and perpendicular to the surface
Surviving dijets: close and tangential to the surface +
punch-through dijets
dihadron
Color strength: yield per unit area
Thickness of the outer corona
single hadron
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2 -fit to all single hadron Raa factors in Au+Au with different centrality bins at RHIC energy
HIJING shadowing + JQ EKS98 shadowing + JQ
),(5.0
),(),,(0 partpart
partpart NsdN
dNNsfNsf
Energy loss parameter
1)397,200( GeVfNormalized in most central Au+Au at 200GeV
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III. Single/dihadron spectra at RHIC/LHC
punch-jets
Surface emission bias
fmGeVFixed /0.50
dihadron
single hadron
At LHC
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Comparisons for shadowing in single hadron spectra in p+A
At RHIC At LHC
4 kinds of shadowing parameterizations, (1)HIJ (S.-Y. Li and X.-N. Wang, PLB527(2002)85-91)
(2)EKS (K.J. Eskola, V.J. Kolhinen and C.A. Salgado, Eur. Phys. J., C9 (1999) 61)
(3)nPDF (M. Hirai, S. Kumano, and T.-H. Nagai, PRC70, (2004) 044905)
(4)nDS (D. de Florian, R. Sassot, PRD69(2004) 074028)
0 Ap
No Quenching! Only shadowing!
Shadowing depends on impact parameter in pA collisions.
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Single/dihadron spectra with different shadowing in A+A at RHIC
Single/dihadron Raa/Iaa are all insensitive to different shadowing at RHIC
dihadronsingle hadron
At RHIC
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Single/dihadron spectra with different shadowing in A+A at LHC
Single hadron Raa insensitive to different shadowing.
Dihadron Iaa sensitive to different shadowing.
At LHC
dihadronsingle hadron
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1) Initial partons participating in strong interaction in central region should be associated with stronger shadowing effects than those initial partons in the outer layer of the system.
2) Because of surface emission bias, single hadron Raa is insensitive to shadowing at RHIC/LHC.
3) Punch-through jets are created from central system region, and where the shadowing is stronger.
4) Punch-through jets at RHIC are greatly suppressed, so dihadron Iaa is also insensitive to shadowing at RHIC.
5) Punch-through jets at LHC are released to dominate dihadron, so dihadron Iaa is sensitive to shadowing at LHC.
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IV. Azimuthal angle anisotropy of single/dihadron spectra at RHIC/LHC
v2 definitions in single/dihadron spectra
dyddpdd
dyddpddp
ThAA
ThAA
Th
2
2
2/
/)2cos()(
Azimuthal anisotropy is
probed by “single jets”.
For dihadron,
dddydydpdpd
dddp
dddydydpdpd
dddp
p
assotrigassoT
trigT
hhAAasso
T
assotrigassoT
trigT
hhAAasso
TtrigT
hh
)2cos(
)(2
Azimuthal anisotropy is
probed by “dijets”.
r
xy Trig
Asso
For single hadron,
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234.6partN 166.6partN
114.2partN 74.4partN
45.5partN 25.7partN
GeVpT 85
Azimuthal angle anisotropy
manifested by jet quenching in high p_T single spectra
jets
single hadron at RHIC
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Dihadron v2 > single hadron v2
single hadron v2
dihadron v2
For single hadron, the anisotropy is probed by quenched single jets which have a bias of surface emission.
For dihadron, the anisotropy is probed by quenched dijets which have a bias of tangential surface emission.
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v2@LHC > v2@RHIC
RHIC
LHC
single hadron v2 dihadron v2
LHC
RHIC
Initial gluon density at LHC > RHIC
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V. Conclusions
1) -fit to both single and dihadron suppression factors
provides a convincing evidence for the jet quenching
description. I_AA is robust to probe the dense matter
when R_AA is fragile.
2) Punch-through jets are found to dominate high p_T dihadron production in Pb+Pb at LHC. Dihadron Iaa at LHC is able to distinguish different shadowing parameterizations.
3) Dihadron v2 > single hadron v2 at RHIC/LHC,and v2@LHC > v2@RHIC for both single/dihadron.
2
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),(),/5.7/()6.1/( 002.1
01
partd
NsfEEdL
dE
1)397,200(),,(5.0
),(,00 GeVfNsdN
dNNsf part
partpart
PHOBOS , nucl-ex/0510042v1, nucl-ex/0604017v1
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Surviving jets contributing to hadron at RHIC
Only vertical surface emission for single hadron
b=0 AuAuat RHIC
single jetsdijets
Tangential surface emission + punch-through for dihadron
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0-10% 10-20%
20-30% 30-40% 40-50%
50-60%
2) Suppression factors vs centrality
0-5%
60-70% 70-80%
single hadron
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nuclear modification factor
dydpdN
dydpdpR
TNN
binary
TAA
TAA 2
2
/
/)(
|)(|)(),(max
min
22maxmin brtrrtbddbbN
b
b AAbinary
)(
2222
/13
)(br
partpart RrrdR
AbNN
dydp
bbd
bbdydp
dN
T
hAA
AAinT
hAA
2maxmin
maxmin2
),(
),(
1
the formula of spectra in AATp
dydpddpbT
dydpdbddpNR
TNN
TAA
TAA
T
partAA 22
222
/)(
/)(
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Invariant mass: 221
2 )( ppM
How to fix scales: M
trigTtrighAAtrigTtrig
assotrigTassoTtrighhAATtrigassotrigTtrig
T
hhAA
trigAA
TAA
TtrigTassoT
dydpddydp
ddydydpdpdpddydydp
dz
dN
NzD
ppz
/
/
1)(
,/
If no medium effects, )()()( TppTdAuTAuAu zDzDzD
(X. –N. Wang , PLB 595(2004)165
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The dihadron azimuthal distributions
trigTtrighAAtrigTtrig
assotrigTassoTtrighhAAassotrigTassoTtrig
hhAA
trigAA dydpddydp
ddydydpdpddydydpdp
d
dN
N /
/1
ddydydpdppp
bbd
bbddydydpdppp
dN
TTTT
hhAA
AAinTTTT
hhAA
212121
maxmin
maxmin212121 2
),(
),(
1
2
212
221
maxmin
maxmin212
221
),(
),(
1
dydydpdp
bbd
bbdydydpdp
dN
TT
hhAA
AAinTT
hhAA
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The ratio between the yield/trigger in AA and in pp:
trigpp
hhpp
trigAA
hhAA
trigpp
hhpp
trigAA
hhAA
yieldpp
partyieldAA
partAA
bb
NN
bNbN
D
NDNI
/
)(/)(
/
)(/)()()(