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Understanding Jet Energy Loss Understanding Jet Energy Loss with Angular Correlation Studies with Angular Correlation Studies
in PHENIXin PHENIX
Ali Hanksfor the PHENIX Collaboration
24th Winter Workshop on Nuclear Dynamics South Padre Island, TX April 8th, 2008
April 8, 2008Ali Hanks - WWND 2
OutlineOutline
• Motivation and some background
• Testing various predictions
• The Near-side "ridge"
• Correlations with photons
• Conclusions
• Understanding the Away-side
• High pT and geometric bias
?
April 8, 2008Ali Hanks - WWND 3
Jet fragmentation in Au+AuJet fragmentation in Au+Au
• Near-side
– jet + ridge (medium response?)
• Away-side– head region (suppressed - jet modification)
– shoulder region (medium response)
p+p Au+Au
April 8, 2008Ali Hanks - WWND 4
ppTT evolution of correlations evolution of correlationsIn
crea
se tr
igge
r p T
Yield enhanced
Shoulder structure remains
Away-sidejet reemerges
arXiv:0801.4545
April 8, 2008Ali Hanks - WWND 5
ppTT evolution of correlations evolution of correlationsIncrease partner pT
Yield suppressed
Away-side jet reemerges
Yield enhanced
Shoulder drops off
arXiv:0801.4545
April 8, 2008Ali Hanks - WWND 6
Away-side head vs shoulderAway-side head vs shoulderdefine head region (HR) as |– | < /6and shoulder region (SR) as /6 < | - | < /2
• Shoulder region:– enhanced for pT< 4GeV/c
– pT spectra appear softer
• Head region:
– suppressed at high pT
– pT spectra steeper at low pT only
April 8, 2008Ali Hanks - WWND 7
Away-side head vs shoulderAway-side head vs shoulder
• Competition between “head” (suppression) and “shoulder” (enhancement)
• Shoulder is important up to ~4 GeV/c
pt,a pt,b < 5
Hard region (jet)
1 < pt,a pt,a < 4
Soft region (medium)
RHS<1
RHS>1
pTa
pTb
arXiv:0801.4545
April 8, 2008Ali Hanks - WWND 8
Away-side compositionAway-side composition
• Shape similar for mesons and baryons– provides constraint on
models describing modification of away-side
• Baryon to Meson ratio similar to the bulk– inconsistent with vacuum
fragmentation
– consistent with jet induced medium excitation
arXiv:0712.3033
April 8, 2008Ali Hanks - WWND 9
Predictions from theoryPredictions from theory
• Cherenkov gluon radiation– measure index of refraction
– peak position has strong pT dependence
Koch, Majumder, Wang, PRL 96 (2006) 172302
• Collective flow coupling
– modification should depend on strength of v2 and path length (?)
Armesto,Salgado,Wiedemann, PRC 72 (2005) 064910
• Mach cone scenarios– measure speed of sound
– peak position has weak pTdependence
Casalderrey-Solana, Shuryak, TeaneyNucl. Phys. A774 (2006) 577
April 8, 2008Ali Hanks - WWND 10
Away-side peak positionsAway-side peak positions
• Fit Method 1:– 2 guassian away-side seperated by D
• Fit Method 2:– 3 guassian away-side
• one fixed by p+p centered at • 2 seperated by D
Weak pT dependence rules out simple gluon radiation models,but is consistent with mach-cone model predictions
arXiv:0801.4545
April 8, 2008Ali Hanks - WWND 11
Peak position vs Reaction planePeak position vs Reaction plane
• Shoulder peak position independent of reaction plane angle
=> insensitive to path length
– consistent with Mach cone scenarios
– poses challenge for models involving jet-flow coupling
Recall from D. Winter's talk
April 8, 2008Ali Hanks - WWND 12
Near-side Near-side
• Broadening in up to pT ≈ 4GeV/c
• Subtracting p+p distribution leaves flat background
– consistent with ~flat ridge + unmodified jet
arXiv:0801.4545
April 8, 2008Ali Hanks - WWND 13
The ridge and shoulder connectionThe ridge and shoulder connection• ridge and shoulder pT spectra are
softer in Au+Au than in p+p– Shoulder is close to inclusive
– ridge may be harder than shoulder
• similar centrality dependence
J. Chen QM08 poster
April 8, 2008Ali Hanks - WWND 14
Going to high pGoing to high pTT - the away-side - the away-side
• Modified jet yield vs pT
– enhancement at low pT
– suppression at high pT
• Shoulder is ehanced up to pT~ 4GeV/c
• Agrees well with expected jet energy loss and induced gluon radiation
Away-side arXiv:0801.4545
April 8, 2008Ali Hanks - WWND 15
Away-side widths at high pAway-side widths at high pTT
• Widths unmodified across centrality bins for high trigger pT
• But broadening is predicted
A. Adare QM2008
April 8, 2008Ali Hanks - WWND 16
Going to higher pGoing to higher pTT - the near-side - the near-side
• Modification of IAA disappears at high
trigger pT
• Widths unmodified at high trigger pT
I AA
I AA
0
A. Adare QM2008
April 8, 2008Ali Hanks - WWND 17
Geometric Bias?Geometric Bias?
• -jet– photon non-interacting so no bias effect on trigger
– possible associated hadron surface bias at high pT
• 2+1 correlations: additional condition of high pT particle on
away-side– reduce surface bias
– still susceptible to tangential bias
trigger
additional away-side particle
partner
tangential bias
surface biasMach coneridge
intermediate pT high pT
Solutions (?):
April 8, 2008Ali Hanks - WWND 18
1/N
trig
dN
/d
(A
.U.)
Run 6 p+p @ 200 GeV
-jet correlations in p+p-jet correlations in p+p• Photon momentum balances with away-side jet
– sensitive to the FF
• Statistical subtraction
– Technique works over large pT range in p+p
– Rγ = N(inclusive γ)/N(decay γ)
Run 6 p+p @ 200 GeV
Per
-Tri
gger
Yie
ld (
A.U
.)
pT trigger
Leading order (LO)
compton annihilation
M. Nguyen QM2008
April 8, 2008Ali Hanks - WWND 19
-jet correlations in Au+Au-jet correlations in Au+Au
Run7 Au+Au 200 GeV12-15 X 3-5 GeV
CF
(A
.U.)
Run7 Au+Au 200 GeV7-9 X 3-5 GeV
CF
(A
.U.)
• Suggests away-side suppresion in Au+Au– sensitive to energy loss of jet
inclusive -h
Direct photon S/B0 peak S/BpQCD accuracy
Near/Away-Side ≈ 1
Near/Away-Side > 1
M. Nguyen QM2008
April 8, 2008Ali Hanks - WWND 20
Fragmentation photonsFragmentation photons
• Medium induced modifications highly sensitive to energy loss of jets
• Direct measurement will improve experimental sensitivity
• p+p measurement important test of pQCD
– LHC--RHIC
Next to leading order (NLO)
Medium induced modifications:
April 8, 2008Ali Hanks - WWND 21
Fragmentation photonsFragmentation photons• First measurement of its kind at
RHIC– next step measure jet shape properties
– ultimately apply procedure to Au+Au
Nfrag/Ninc ≈ 0.1 at intermediate pT
A. Hanks QM08 poster
April 8, 2008Ali Hanks - WWND 22
ConclusionsConclusions
Modification to two particle correlations seen in Au+Au collisions on both the near and away-side
– away-side pT dependence consistent with mach cone scenario
while challenging gluon radiation and deflected jet models
– modification at intermediate pT suggests dominance of jet
induced medium excitations
– high pT dominated by jet fragmentation
• away-side suppresion consistent with energy loss
• unmodified near-side and no observation of broadening in away-side suggests geometric bias
– -jet and h- correlations can provide new insight
April 8, 2008Ali Hanks - WWND 26
Near-side modificationNear-side modification
• Enhancement at low pT
• "Suppression" at high associated pT
and low trigger pT
– dillusion effect?
• Broadening in at low trigger and associated pT
• Agrees with p+p at high pT