Understanding Jet Energy Loss with Angular Correlation Studies in PHENIX Ali Hanks for the PHENIX Collaboration 24 th Winter Workshop on Nuclear Dynamics South Padre Island, TX April 8th, 2008

Ali Hanks - WWND April 8, 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 Near-side –jet + ridge (medium response?) Away-side –Head region (suppressed - jet modification) –Shoulder region (medium response) p+pAu+Au

Ali Hanks - WWND April 8, 2008 p T evolution of correlations Increase trigger p T Yield enhanced Shoulder structure remains Jet reemerges

Ali Hanks - WWND April 8, 2008 p T evolution of correlations Increase partner p T Yield suppressed Jet reemerges Yield enhanced

Ali Hanks - WWND April 8, 2008 Away-side modification Modified jet yield vs p T –enhancement at low p T –suppression at high p T Agrees well with expected jet energy loss and induced gluon radiation Shoulder is ehanced up to p T ~ 4GeV/c I AA

Ali Hanks - WWND April 8, 2008 Away-side head vs shoulder Shoulder enhanced up to p T ≈ 4GeV/c

Ali Hanks - WWND April 8, 2008 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 Weak p T dependence best explained by mach-cone models

Ali Hanks - WWND 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 p T ≈ 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 p T 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

Ali Hanks - WWND April 8, 2008 Going to high p T Suppression at high p T agrees with jet energy loss expectations Widths unmodified within errors I AA But broadening is predicted

Ali Hanks - WWND April 8, 2008 Geometric Bias?  -jet –photon non-interacting so no bias effect on trigger –possible associated hadron surface bias at high p T 2+1 correlations: additional condition of high p T particle on away- side –reduce surface bias –still susceptible to tangential bias trigger additional away-side particle partner tangential bias surface bias Mach cone ridge intermediate p T high p T Solutions (?):

Ali Hanks - WWND April 8, /Ntrig dN/d  (A.U.) Run GeV  -jet correlations in p+p Photon momentum balances with away-side jet –sensitive to the FF Statistical subtraction –Technique works over large p T range in p+p –Rγ = N(inclusive γ)/N(decay γ) Run GeV Per-Trigger Yield (A.U.) p T trigger Leading order (LO) comptonannihilation

Ali Hanks - WWND April 8, 2008  -jet correlations in Au+Au Run7 Au+Au 200 GeV X 3-5 GeV CF (A.U.) Run7 Au+Au 200 GeV 7-9 X 3-5 GeV CF (A.U.) Suggests away-side suppresion in Au+Au –sensitive to energy loss of jet inclusive  -h

Ali Hanks - WWND April 8, 2008 Fragmentation 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:

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 N frag /N inc ≈ 0.1 at intermediate p T

Ali Hanks - WWND April 8, 2008 Conclusions Modification to two particle correlations seen in Au+Au collisions on both the near and away-side –away-side p T dependence consistent with mach cone scenario while challenging gluon radiation and deflected jet models –modification at intermediate p T suggests dominance of jet induced medium excitations –high p T 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

Ali Hanks - WWND April 8, 2008 Backup Slides

Ali Hanks - WWND April 8, correlations

Ali Hanks - WWND April 8, 2008 Near-side modification Enhancement at low p T "Suppression" at high associated p T and low trigger p T –dillusion effect? I AA Broadening in Df at low trigger and associated p T Agrees with p+p at high p T

Ali Hanks - WWND April 8, 2008 Near side composition

Ali Hanks - WWND April 8, 2008 Going to higher p T - the near-side I AA

Ali Hanks - WWND April 8, 2008 Ridge cont'd

Ali Hanks - WWND April 8, 2008 Ridge vs Shoulder cont'd nucl-ex Near-side Away-side

Ali Hanks - WWND April 8, 2008 Predictions from theory