Understanding Jet Energy Loss with Angular Correlation Studies in PHENIX Ali Hanks for the PHENIX Collaboration 24 th Winter Workshop on Nuclear Dynamics

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

?


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

Away-sidejet reemerges

arXiv:0801.4545


ppTT evolution of correlations evolution of correlationsIncrease partner pT

Yield suppressed

Away-side jet reemerges

Yield enhanced

Shoulder drops off

arXiv:0801.4545


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


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


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


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


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


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


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


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


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


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


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


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

M. Nguyen QM2008


-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


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 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


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


head vs shoulder in centralityhead vs shoulder in centrality


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


Near side compositionNear side composition


Ridge vs Shoulder cont'dRidge vs Shoulder cont'd

0712.3033 nucl-ex

Near-side

Away-side

Documents

Understanding Jet Energy Loss with Angular Correlation Studies in PHENIX Ali Hanks for the PHENIX Collaboration 24 th Winter Workshop on Nuclear Dynamics