Study Jet Energy Loss with 2 particle Correlations

Study Jet Energy Loss with 2 -particle Correlations Hua Pei Iowa State University For PHENIX at RHIC Ø How back-to-back jets lose energy Ø Different p. T region of jet energy loss Ø Changing surface bias: 2+1 particle correlation Hua Pei of ISU for PHENIX at QM 08

We know Jet Quenches in AA relative to p+p, and we measure per-trigger yield ar. Xiv: 0801. 4545 v 1 [nucl-ex] More central 0 -20% Au+Au 20 -40% 60 -92% Solid points are Au+Au, open points are p+p, red/blue colors show systematic errors. Hua Pei of ISU for PHENIX at QM 08

A Jet Function Can Be Divided into Regions ar. Xiv: 0801. 4545 v 1 [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 talk M. Mc. Cumber Hua Pei of ISU for PHENIX at QM 08

We Measure the Central Au+Au Jet Spectrum at Head Region and Compare to p+p ar. Xiv: 0801. 4545 v 1 [nucl-ex] Each panel shows a different p. Ta (trigger), and plotted as function of p. Tb (assoc) Hua Pei of ISU for PHENIX at QM 08

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 QM 08

The Modification of per-trigger Yield (IAA) has strong assoc p. T Dependence ar. Xiv: 0801. 4545 v 1 [nucl-ex] At high p. Ta and p. Tb, IAA ≈ RAA (inclusive) at head region. Quantified suppression of far-side jet => further constraint on e-loss. Hua Pei of ISU for PHENIX at QM 08

Compare Jet Spectrum (mean p. T) of Head Region to Inclusive Spectrum ar. Xiv: 0801. 4545 v 1 [nucl-ex] “Punch-through” of jet at highest p. T? At most central collisions, the mean p. T of Head Region approaches the inclusive spectrum (gray line near bottom of each panel) Hua Pei of ISU for PHENIX at QM 08

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 QM 08

JAA pair suppression ar. Xiv: 0801. 4545 v 1 [nucl-ex] • JAA is suppressed at high p. T at all centralities. • At all centralities, JAA ≈ RAA 2 (dashed line) at highest p. Ta, b, indicating both trigger/assoc are suppressed. Hua Pei of ISU for PHENIX at QM 08

Relative energy loss back-to-back jet Relates ratio of particle p. T Spectrum in the form of m (multiplicity), n (slope), x. E, and xh measured Ratio of MEAN parton transverse momentum Be fitted from spectrum Hua Pei of ISU for PHENIX at QM 08 PHYSICAL REVIEW D 74, 072002 (2006)

The spectrum is fitted to get x^ h Hua Pei of ISU for PHENIX at QM 08

Compare Au+Au ^x to p+p x^ 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 Shown by Michael J. Tannenbaum DNP 07 Hua Pei of ISU for PHENIX at QM 08

Change the surface-bias of near-side? Select events that have both a high-pt p 0 and a back-to-back hadron (back-hemisphere of p 0 ) Trigger p 0 Assoc h Trigger p 0 Medium “Conditional” charged hadron at high-pt Path lengths comparable in dense medium. A. k. a. , 2+1 correlations Assoc h Removes some events where hard-scattering occurs near surface but not tangential (large difference between path lengths) Shift distribution of hard scattering towards center of medium. Near-side parton travels through more medium Hua Pei of ISU for PHENIX at QM 08

This 2+1 changes near-side jets of both p+p and Cu+Cu l Per-trigger yield of p+p on near side increase with conditional particle p. T. l Expected in p+p! Higher Q 2 comes with higher p. T away-side particle. l In Cu+Cu the yield also increases but not same slope as in p+p. Hua Pei of ISU for PHENIX at QM 08

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 QM 08

Another handle on path-length: Reaction plane dependence In-Plane Out-Plane Evolution of “Head Region” is observed. Need more work to quantify that Hua Pei of ISU for PHENIX at QM 08

Conclusion • Jets are affected by medium, on both near and far side. • Medium effect on jets vary on centrality and p. T. • 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 QM 08 and near future. Hua Pei of ISU for PHENIX at QM 08

Back up Hua Pei of ISU for PHENIX at QM 08

The Modification of per-trigger Yield (IAA) has strong assoc p. T Dependence ar. Xiv: 0801. 4545 v 1 [nucl-ex] At high p. Ta and p. Tb, IAA ≈ RAA (inclusive) at head region. Quantifies suppression of far-side jet => further constraint on e-loss. Hua Pei of ISU for PHENIX at QM 08

The IAA of both “Head” and “Head + Shoulder” ar. Xiv: 0801. 4545 v 1 [nucl-ex] At high p. Ta and p. Tb, IAA ≈ RAA (inclusive) at head region Hua Pei of ISU for PHENIX at QM 08

The mean p. T as a function of p. TB range ar. Xiv: 0801. 4545 v 1 [nucl-ex] Hua Pei of ISU for PHENIX at QM 08

Source of formula on xh PHYSICAL REVIEW D 74, 072002 (2006) Hua Pei of ISU for PHENIX at QM 08