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 2 April 8, 2008 Outline Motivation and some background Testing various predictions The Near-side "ridge" Correlations with photons Conclusions Understanding the Away-side High p T and geometric bias ?  

Ali Hanks - WWND 3 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 4 April 8, 2008 p T evolution of correlations Increase trigger p T Yield enhanced Shoulder structure remains Away-side jet reemerges arXiv:

Ali Hanks - WWND 5 April 8, 2008 p T evolution of correlations Increase partner p T Yield suppressed Away-side jet reemerges Yield enhanced Shoulder drops off arXiv:

Ali Hanks - WWND 6 April 8, 2008 Away-side head vs shoulder define head region (HR) as |  –  | <  /6 and shoulder region (SR) as  /6 < |  -  | <  /2 Shoulder region: –enhanced for p T < 4GeV/c –p T spectra appear softer Head region: – suppressed at high p T –p T spectra steeper at low p T only

Ali Hanks - WWND 7 April 8, 2008 Away-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) R HS <1 R HS >1 pTapTa pTbpTb arXiv:

Ali Hanks - WWND 8 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 –inconsistent with vacuum fragmentation –consistent with jet induced medium excitation arXiv:

Ali Hanks - WWND 9 April 8, 2008 Predictions from theory Cherenkov gluon radiation –measure index of refraction –peak position has strong p T dependence Koch, Majumder, Wang, PRL 96 (2006) Collective flow coupling –modification should depend on strength of v 2 and path length (?) Armesto,Salgado,Wiedemann, PRC 72 (2005) Mach cone scenarios –measure speed of sound –peak position has weak p T dependence Casalderrey-Solana, Shuryak, Teaney Nucl. Phys. A774 (2006) 577

Ali Hanks - WWND 10 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 rules out simple gluon radiation models, but is consistent with mach-cone model predictions arXiv:

Ali Hanks - WWND 11 April 8, 2008 Peak 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

Ali Hanks - WWND 12 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 arXiv:

Ali Hanks - WWND 13 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 similar centrality dependence J. Chen QM08 poster

Ali Hanks - WWND 14 April 8, 2008 Going to high p T - the away-side Modified jet yield vs p T –enhancement at low p T –suppression at high p T Shoulder is ehanced up to p T ~ 4GeV/c Agrees well with expected jet energy loss and induced gluon radiation Away-side arXiv:

Ali Hanks - WWND 15 April 8, 2008 Away-side widths at high p T Widths unmodified across centrality bins for high trigger p T But broadening is predicted A. Adare QM2008

Ali Hanks - WWND 16 April 8, 2008 Going to higher p T - the near-side Modification of I AA disappears at high trigger p T Widths unmodified at high trigger p T I AA 0 A. Adare QM2008

Ali Hanks - WWND 17 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 18 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 M. Nguyen QM2008

Ali Hanks - WWND 19 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 Direct photon S/B  0 peak S/B pQCD accuracy Near/Away-Side ≈ 1 Near/Away-Side > 1 M. Nguyen QM2008

Ali Hanks - WWND 20 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 21 April 8, 2008 Fragmentation photons First measurement of its 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 A. Hanks QM08 poster

Ali Hanks - WWND 22 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 23 April 8, 2008 Backup Slides

Ali Hanks - WWND 24 April 8, correlations

Ali Hanks - WWND 25 April 8, 2008 head vs shoulder in centrality

Ali Hanks - WWND 26 April 8, 2008 Near-side modification Enhancement at low p T "Suppression" at high associated p T and low trigger p T –dillusion effect? Broadening in  at low trigger and associated p T Agrees with p+p at high p T

Ali Hanks - WWND 27 April 8, 2008 Near side composition

Ali Hanks - WWND 28 April 8, 2008 Ridge vs Shoulder cont'd nucl-ex Near-side Away-side