1 Mapping out the Jet correlation landscape: Perspective from PHENIX Jiangyong Jia for PHENIX Collaboration Stony Brook University & BNL 23th WWND Big Sky, MT February 11-18, 2007

2 Trigger and associated pT Away jet I AA Thermallized gluon radiation Shock wave or cherenkov? flow, Jet broadening Punch through jets or tangential contribution? Correlation landscape in pT1, pT2 T 3T I IIIII IV Rich interactions between jet and medium Low pTModerately high pT Intermediate pThigh pT Main goal is to understand: Quenching of the jet by the medium Response of the medium to the jet

3 Evolution with pT1,pT2 Away jet shape: broaden shape -> dip -> broaden shape -> peak Dip grows Jet emerges PHENIX Preliminary

4 Pt,2 Pt,1 Cone Flat peak p t,1 p t,2 >  4 1  <p t,1 p t,2 <  4

5 Pt,2 Pt,1 Cone Flat peak p t,1 p t,2 >  4 1  <p t,1 p t,2 <  4 Competition between “Head” and “shoulder”. Head region: Suppression of jet Shoulder Region: Response of the medium

6 Location of the “displaced” peaks D  1, independent of centrality (at N part >100), collision system and √s. D D Independent of pT (when not dominated by head region) nucl-ex/

7 Relative amplitude of Head/Shoulder: pT dependence More concave pT More concave for increasing pT (in a limited range)

8 Relative amplitude of Head/Shoulder: Centrality dependence More concave for increasing N part More concave Npart peripheral central

9 Broad or displaced peak is seen for different energies. Relative amplitude of Head/Shoulder: √s dependence nucl-ex/ More concave √s =17.2 √s =62.4√s =200 √s More concave with increasing √s.

10 Relative amplitude of Head/Shoulder: √s dependence Peak ~ 0.17, Min ~0.07 |  |<0.35

11 Peak ~ 0.07, Min ~0.06  CM <0.7 Relative amplitude of Head/Shoulder: √s dependence Peak ~ 0.17, Min ~0.07 Shoulder 200 GeV  2.5x Shoulder 17.2 GeV Head 200 GeV  Head 17.2 GeV |  |<0.35 Head: Jet dominate! Jet multiplicity at SPS is lower, but less quenching Shoulder: Weaker medium response at SPS ?

12 A possible picture Head region: Suppression of jet Fragmentation of surviving jet and its radiated gluons Shoulder Region: Dissipation of the lost energy in medium Cherenkov/Mach Shock/Deflected jet Increase pt Cherenkov: wrong pT dependence Mach Shock + jet Deflected jet: models need to describe the pT dependence (Hydro wake, Hwa’s MPS model, large angle rad.)

13 Chemistry of the Shoulder/Cone? Triggering on high pT and identify the associated hadrons Cone shape observed for associated baryons, but away side is flatter than mesons. 0-20% 2.5-4x1.6-2 GeV/c Baryon/meson increase with pT and centrality Jet frag.<Bayron/meson<  bulk medium.

14 Chemistry of the Shoulder? u d u u d uu d d u uu d d u Bulk medium are boosted by shock wave, which then coalesce into hadrons? => jet frag.<Bayron/meson<Bulk Cooper-Fryer

15 Quantify the yield: I AA Integrate the yield in near side: |  |<  /3, away side: |  |<  /2, and make I AA = Y AA /Y PP

16 I AA = Y AA /Y PP Enhancement at low p T,assoc due to “shoulder” Suppression at large p T,assoc due to “head” Away side

17 I AA = Y AA /Y PP Strong modification persists to high pT trigger Away side Shoulder enhancement Head suppression Away side Competition between enhancement in the Shoulder region and suppression in the Head region. Jet narrows as function of p T,trig, p T,assoc. The fraction of jet fragmentation and gluon radiation ends up in the “Head” region is larger. Jet (“Head”) spectra in p T,assoc is harder than medium (“Shoulder”), shoulder enhancement limited to 4 GeV/c

18 I AA = Y AA /Y PP Enhancement at low p T,assoc Suppression at large p T,assoc Near side

19 I AA = Y AA /Y PP Modifications decrease with increasing trigger pT (flattening) Near side 8<p T,t <15GeV/c zTzT STAR Ridge enhancement Note: PHENIX ridge yield is smaller than STAR due to smaller  range (PHENIX:|  |<0.35, STAR:|  |<1) Modification limited to p T,trig, p T,assoc <4 GeV/c, similar to the range for away side cone. STAR: This is due to near side ridge

20 Near side width Trigger p T = x 2-3 GeV/c Ridge is also reflected in the broadening of the near side width at intermediate pT

21 Sources of “jet” pairs One usually find only one “jet” pair per event. “Jet” is statistical sum of different types of signals Near jet Ridge Cone Away jet L~0 L<R L~2R 0 <L<2R Three particle correlation signal sum of Different geometrical bias and trigger bias 0 

22 Sources of “jet” pairs Near jet Ridge Cone Away jet L~0 L<R L~2R 0 <L<2R Medium response + reco Jet fragmentation + radiation 0 

23 Ridge vs cone: different medium response? Both important up to 4 GeV/c in p T,trig, p T,assoc. Softer than jet. Both have particle composition close to bulk. Ridge width in  is broader than jet, but no displaced peak. Same origin: due to different ? Ridge is a premature cone (T.Renk). Cone also elongated in  (T.Renk), but hidden by  swing. Different origin: Away side should also have a ridge, centered around the “Head” region.

24 Compare the pT1,pT2, PID, charge, √s dependence of the shape and yield for ridge and cone. If ridge is medium response, it’s charge dependence very different from near side jet. Should have less charge ordering effect. √s can tell us how the medium effect turns on and how it competes with the jet quenching. More quenching->stronger medium response. Distinguish the ridge and cone Dial the of near and away side jet with multi-par.corr. (T.Renk) Trig on two back-back high pT particle, and correlate with soft particle? Note: Possible only if the high pT away side have significant punch-though component Tangential emission trig1trig2 assoc

25 Correlation at very low pT Away “Cone” shape seen for low pt-low pt correlations in central Au+Au (Npart>100) Correlation among soft particles generated or boosted by jets? Why no near side ridge structure? 200 GeV Au+Au, 0-5% Central PHENIX Preliminary 0.2 < p T,1 < 0.4 GeV/c, 0.2 < p T,2 < 0.4 GeV/c, |  |<0.1 Like-Sign Pairs Unlike-Sign Pairs

26 Comments on flow background subtraction v 2 {2}, v 2 {4}, v 2 {RP}, v 2 {v1RP} etc. PHENIX use the v2{RP}, where RP determined in 3<|  |<4 STAR use the average between v 2 {RP} and v2{4}. CF = J(  ) +  (1+2 cos2  ) Two-particle correlation automatically includes all non-flow and e-b-e fluctuations. So v2{2} should be used, except that non- flow due to jet need to be removed since it is the signal. PHENIX v2{RP} is not affected by jet ( nucl-ex/ ). But it measures in fact: v2{4} is too small because it removes the ebe eccentricity fluctuations. ( P. Sorensen QM06 talk ). STAR use a smaller v2 in bg subtraction than PHENIX

27 Backup

28 Which v2 should be used? The non-flow/v2 fluctuation effects (if any) contributes to the flow background. Exception is v2 bias from jets. CF = J(  ) +  (1+2v 2 t v 2 a cos2  ) Physical v2   part.

29 physics is driven by the ebe rotated RP: v2{2} should be used (modulo removing jet bias). Which v2 should be used? Rajeev,Ollitrault, PLB 641:260,2006. v2{EP} does not include v2 fluctuation systematically too small.

30 Non-flow/bias effect due to jets 1)HIJING events are randomly assigned a RP direction and particles are weighted according to the experimental measured v2(pT,  ) 2)Embed pythia di-jet events (trigger >6 GeV/c) into the HIJING with flow Jet bias should be small at BBC (3<|  <4), we confirm it with simulation Event nucl-ex/

31 The perturbation in Reaction Plane is correlated with the jet direction. This leads to a fake v2 (non-flow) of the jet at mid-rapidity This fake v2 depends on the multiplicity and eccentricity. Large bias small bias Distribution of mid-rapidity triggers respective to the RP determined in 0.8<  <2.8 Before embedding After embedding Fake v2 generated!

32 Fake v2 of the high pT triggers Note, the true v2 of trigger is  2.8 Central Peripheral 1.0    2.8

33 Jet multiplicity is modified, so we embed pythia doubling the jet multiplicity.