Transcript Understanding Jet Energy Loss with Angular Correlation

Understanding Jet Energy Loss
with Angular Correlation Studies
in PHENIX
Ali Hanks
for the PHENIX Collaboration
24th Winter Workshop on
Nuclear Dynamics
South Padre Island, TX
April 8th, 2008
Outline
• Motivation and some background
• Away-side "Mach-cone" effect
• Near-side "ridge"
• Correlations with photons
• Conclusions
Ali Hanks - WWND
April 8, 2008
Jet fragmentation in Au+Au
p+p
Au+Au
• Near-side
– jet + ridge (medium response?)
• Away-side
– Head region (suppressed - jet modification)
– Shoulder region (medium response)
Ali Hanks - WWND
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pT evolution of correlations
Increase trigger pT
Yield enhanced
Shoulder structure
remains
Jet reemerges
Ali Hanks - WWND
April 8, 2008
pT evolution of correlations
Increase partner pT
Yield enhanced
Yield suppressed
Jet reemerges
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April 8, 2008
Away-side modification
• Modified jet yield vs pT
– enhancement at low pT
– suppression at high pT
• Agrees well with expected
jet energy loss and induced
gluon radiation
• Shoulder is ehanced up to
pT~ 4GeV/c
Ali Hanks - WWND
April 8, 2008
Away-side head vs shoulder
• Shoulder enhanced up to
pT ≈ 4GeV/c
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Away-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
Ali Hanks - WWND
Weak pTdependence best
explained by mach-cone
models
April 8, 2008
Away-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
– incosistent with vacuum
fragmentation
– consistent with jet induced
medium excitation
Ali Hanks - WWND
April 8, 2008
Near-side 
• Broadening in 
up to pT ≈ 4GeV/c
• Subtracting p+p
distribution leaves
flat background
– consistent with ~flat
ridge + unmodified
jet
Ali Hanks - WWND
April 8, 2008
The 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
• ridge and shoulder balance
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April 8, 2008
Going to high pT
• Suppression at high pT agrees with
jet energy loss expectations
IAA
• Widths unmodified within errors
• But broadening is
predicted
Ali Hanks - WWND
April 8, 2008
Geometric Bias?
intermediate pT
high pT
tangential bias
ridge
surface bias
Mach cone
Solutions (?):
• -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 awayside
– reduce surface bias
– still susceptible to tangential bias
Ali Hanks - WWND
trigger
partner
additional away-side
particle
April 8, 2008
-jet correlations in p+p
• Photon momentum balances with away-side jet
Leading order (LO)
– sensitive to the FF
• Statistical subtraction
– Technique works over large pT range in p+p
– Rγ = N(inclusive γ)/N(decay γ)
1/Ntrig dN/d(A.U.)
Per-Trigger Yield (A.U.)
compton
annihilation
Run 6 p+p @ 200 GeV
Run 6 p+p @ 200 GeV
pT trigger
Ali Hanks - WWND
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-jet correlations in Au+Au
CF (A.U.)
– sensitive to energy loss of jet
inclusive -h
CF (A.U.)
• Suggests away-side suppresion
in Au+Au
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Run7 Au+Au 200 GeV
7-9 X 3-5 GeV
Run7 Au+Au 200 GeV
12-15 X 3-5 GeV
Fragmentation photons
Next to leading order (NLO)
– LHC
--RHIC
Medium induced modifications:
• Medium induced modifications highly
sensitive to energy loss of jets
• Direct measurement will improve
experimental sensitivity
• p+p measurement important test of pQCD
Ali Hanks - WWND
April 8, 2008
Fragmentation photons
• First measurement of it's kind at
RHIC
– next step measure jet shape properties
– ultimately apply procedure to Au+Au
Nfrag/Ninc ≈ 0.1 at intermediate pT
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April 8, 2008
Conclusions
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 awayside suggests geometric bias
– -jet and h- correlations can provide new insight
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Backup Slides
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2+1 correlations
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Near-side modification
• Broadening in Df at low trigger
and associated pT
IAA
• Agrees with p+p at high pT
• Enhancement at low pT
• "Suppression" at high associated
pT and low trigger pT
– dillusion effect?
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April 8, 2008
Near side composition
Ali Hanks - WWND
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IAA
Going to higher pT - the near-side
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Ridge cont'd
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Ridge vs Shoulder cont'd
0712.3033 nucl-ex
Near-side
Away-side
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Predictions from theory
Ali Hanks - WWND
April 8, 2008