Study Jet Energy Loss with 2-particle Correlations

1. Study Jet Energy Loss with 2-particle Correlations Hua Pei Iowa State University For PHENIX at RHIC • How back-to-back jets lose energy • Different pT region of jet energy loss • Changing surface bias: 2+1 particle correlation Hua Pei of ISU for PHENIX at QM08

2. 0-20% Au+Au 20-40% 60-92% Solid points are Au+Au, open points are p+p, red/blue colors show systematic errors. We know Jet Quenches in AA relative to p+p, and we measure per-trigger yield More central arXiv:0801.4545v1 [nucl-ex] Hua Pei of ISU for PHENIX at QM08

3. A Jet Function Can Be Divided into Regions arXiv:0801.4545v1 [nucl-ex] We define “HR”, the head region, as |Df – p| < p /6 This HR is where we expected the away-side jet appears. For region “SR”, given in parallel talkM. McCumber Hua Pei of ISU for PHENIX at QM08

4. We Measure the Central Au+Au Jet Spectrum at Head Region and Compare to p+p arXiv:0801.4545v1 [nucl-ex] Each panel shows a different pTa (trigger), and plotted as function of pTb (assoc) Hua Pei of ISU for PHENIX at QM08

5. We use IAA to quantify the change of jet spectrum IAA is defined as the modification of per-trigger yield Yjet_ind, of AA relative to p+p. Hua Pei of ISU for PHENIX at QM08

6. The Modification of per-trigger Yield (IAA) has strong assoc pT Dependence arXiv:0801.4545v1 [nucl-ex] At high pTa and pTb, IAA ≈ RAA (inclusive) at head region. Quantified suppression of far-side jet => further constraint on e-loss. Hua Pei of ISU for PHENIX at QM08

7. Compare Jet Spectrum (mean pT) of Head Region to Inclusive Spectrum arXiv:0801.4545v1 [nucl-ex] “Punch-through” of jet at highest pT? At most central collisions, the mean pT of Head Region approaches the inclusive spectrum (gray line near bottom of each panel) Hua Pei of ISU for PHENIX at QM08

8. JAA is used to measure the change of particle pairs induced by di-jet • JPY is the number of di-hadron pairs (both particles from jet) per event. • JAA is the ratio of JPY of AA to p+p, normalized by Ncoll • Thus by definition, JAA = IAA* RAA Hua Pei of ISU for PHENIX at QM08

9. JAA pair suppression arXiv:0801.4545v1 [nucl-ex] • JAA is suppressed at high pTat all centralities. • At all centralities, JAA ≈ RAA2 (dashed line) at highest pTa,b, indicating both trigger/assoc are suppressed. Hua Pei of ISU for PHENIX at QM08

10. Relates ratio of particle pT measured Spectrum in the form of m (multiplicity), n (slope), xE, and xh Relative energy loss back-to-back jet Ratio of MEAN parton transverse momentum PHYSICAL REVIEW D 74, 072002 (2006) Be fitted from spectrum Hua Pei of ISU for PHENIX at QM08

11. ^ The spectrum is fitted to get xh Hua Pei of ISU for PHENIX at QM08

12. ^ ^ ^ The Au+Au xh ~ 0.5-0.6 relative to p+p, If no suppression happened to partons in medium, this ratio shall be 1 => Larger energy loss on away-side due to medium Compare Au+Au x to p+p x Shown by Michael J. Tannenbaum DNP07 Hua Pei of ISU for PHENIX at QM08

13. Trigger p0 Trigger p0 Medium “Conditional” charged hadron at high-pt Assoc h Assoc h Change the surface-bias of near-side? Select events that have botha high-pt p0and a back-to-back hadron (back-hemisphere of p0 ) Removes some events where hard-scattering occurs near surface but not tangential (large difference between path lengths) Path lengths comparable in dense medium. A.k.a., 2+1 correlations Shift distribution of hard scattering towards center of medium. Near-side parton travels through more medium Hua Pei of ISU for PHENIX at QM08

14. This 2+1 changes near-side jets of both p+p and Cu+Cu • Per-trigger yield of p+p on near side increase with conditional particle pT. • Expected in p+p! HigherQ2comes withhigher pT away-side particle. • In Cu+Cu the yield also increases but not same slope as in p+p. Hua Pei of ISU for PHENIX at QM08

15. Centrality dependence of near-side yields Cu+Cu yield increases from central (left) to peripheral (right) in each bin and approaches p+p (most right point in each bin) The fact that Cu+Cu yield is reduced at central is possibly due to 1) weaker surface-bias, 2) more “+1” particles from underlying event Hua Pei of ISU for PHENIX at QM08

16. In-Plane Out-Plane Another handle on path-length: Reaction plane dependence Evolution of “Head Region” is observed. Need more work to quantify that Hua Pei of ISU for PHENIX at QM08

17. Conclusion • Jets are affected by medium, on both near and far side. • Medium effect on jets vary on centrality and pT. • Thus, we quantify the medium effects as the suppression of jet, using per-trigger-yield, I_AA, J_AA. This suppression shows strong indication of jet particle sources at different kinetic region. • 2+1 correlation brings another method of controlling jet source via the surface-bias, especially on exploring the near side jet suppression. • PHENIX has the brand new 2007 Au+Au data and we are showing many more results in this QM08 and near future. Hua Pei of ISU for PHENIX at QM08

18. Back up Hua Pei of ISU for PHENIX at QM08

19. The Modification of per-trigger Yield (IAA) has strong assoc pT Dependence arXiv:0801.4545v1 [nucl-ex] At high pTa and pTb, IAA ≈ RAA (inclusive) at head region. Quantifies suppression of far-side jet => further constraint on e-loss. Hua Pei of ISU for PHENIX at QM08

20. The IAA of both “Head” and “Head + Shoulder” arXiv:0801.4545v1 [nucl-ex] At high pTa and pTb, IAA ≈ RAA (inclusive) at head region Hua Pei of ISU for PHENIX at QM08

21. The mean pT as a function of pTB range arXiv:0801.4545v1 [nucl-ex] Hua Pei of ISU for PHENIX at QM08

22. Source of formula on xh PHYSICAL REVIEW D 74, 072002 (2006) Hua Pei of ISU for PHENIX at QM08