Understanding Jet Energy Loss with Angular Correlation Studies in PHENIX

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

OutlineOutline

• Motivation and some background

• Away-side "Mach-cone" effect

• Near-side "ridge"

• Correlations with photons

• Conclusions


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


ppTT evolution of correlations evolution of correlationsIn

crea

se tr

igge

r p T

Yield enhanced

Shoulder structure remains

Jet reemerges


ppTT evolution of correlations evolution of correlationsIncrease partner pT

Yield suppressed

Jet reemerges

Yield enhanced


Away-side modificationAway-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

I AA


Away-side head vs shoulderAway-side head vs shoulder

• Shoulder enhanced up to pT ≈ 4GeV/c


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 pTdependence best explained by mach-cone models


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– incosistent with vacuum

fragmentation

– consistent with jet induced medium excitation


Near-side Near-side • Broadening in

up to pT ≈ 4GeV/c

• Subtracting p+p distribution leaves flat background

– consistent with ~flat ridge + unmodified jet


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

• ridge and shoulder balance


Going to high pGoing to high pTT

• Suppression at high pT agrees with

jet energy loss expectations

• Widths unmodified within errorsI AA

• But broadening is predicted


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 (?):


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


-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


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:


Fragmentation photonsFragmentation 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


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


Backup SlidesBackup Slides


2+1 correlations2+1 correlations


Near-side modificationNear-side modification

• Enhancement at low pT

• "Suppression" at high associated pT

and low trigger pT

– dillusion effect?

I AA

• Broadening in Df at low trigger and associated pT

• Agrees with p+p at high pT


Near side compositionNear side composition


Going to higher pGoing to higher pTT - the near-side - the near-sideI A

A


Ridge cont'dRidge cont'd


Ridge vs Shoulder cont'dRidge vs Shoulder cont'd

0712.3033 nucl-ex

Near-side Away-side


Predictions from theoryPredictions from theory

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Understanding Jet Energy Loss with Angular Correlation Studies in PHENIX

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