study jet energy loss with 2-particle correlations
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Hua Pei of ISU for PHENIX at QM08 1
Study Jet Energy Loss with 2-particle Correlations
How back-to-back jets lose energy
Different pT region of jet energy loss
Changing surface bias: 2+1 particle correlation
Hua Pei
Iowa State University
For PHENIX at RHIC
Hua Pei of ISU for PHENIX at QM08 2
We know Jet Quenches in AA relative to p+p, and we measure per-trigger yield
0-20% Au+Au 20-40% 60-92%
Solid points are Au+Au, open points are p+p, red/blue colors show systematic errors.
More central arXiv:0801.4545v1[nucl-ex]
Hua Pei of ISU for PHENIX at QM08 3
A Jet Function Can Be Divided into Regions
We define “HR”, the head region, as | – | < /6
This HR is where we expected the away-side jet appears.
For region “SR”, given in parallel talk M. McCumber
arXiv:0801.4545v1[nucl-ex]
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
Each panel shows a different pTa (trigger), and
plotted as function of pTb (assoc)
arXiv:0801.4545v1[nucl-ex]
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
At high pTa and pT
b, IAA ≈ RAA (inclusive) at head region.
Quantified suppression of far-side jet => further constraint on e-loss.
arXiv:0801.4545v1[nucl-ex]
Hua Pei of ISU for PHENIX at QM08 7
Compare Jet Spectrum (mean pT) of Head Region to Inclusive Spectrum
At most central collisions, the mean pT of Head Region approaches the inclusive spectrum (gray line near bottom of each panel)
“Punch-through” of jet at highest pT?
arXiv:0801.4545v1[nucl-ex]
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
• JAA is suppressed at high pT at all centralities.
• At all centralities, JAA ≈ RAA2 (dashed line) at highest pT
a,b, indicating both trigger/assoc are suppressed.
arXiv:0801.4545v1[nucl-ex]
Hua Pei of ISU for PHENIX at QM08 10
Relative energy loss back-to-back jet
Ratio of MEAN parton transverse momentum
Be fitted from spectrum
measured
Relates ratio of particle pT
PHYSICAL REVIEW D 74, 072002 (2006)
Spectrum in the form of m (multiplicity), n (slope), xE, and xh
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
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 DNP07
^
Hua Pei of ISU for PHENIX at QM08 13
Change the surface-bias of near-side?
Select events that have both a high-pt 0 and a back-to-back hadron (back-hemisphere of 0 )Trigger 0
“Conditional”
charged hadron
at high-pt
MediumAssoc h
Trigger 0
Assoc h
Shift distribution of hard scattering towards center of medium. Near-side parton travels through more medium
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
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! Higher Q2 comes with higher 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
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 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
At high pTa and pT
b, IAA ≈ RAA (inclusive) at head region.
Quantifies suppression of far-side jet => further constraint on e-loss.
arXiv:0801.4545v1[nucl-ex]
Hua Pei of ISU for PHENIX at QM08 20
The IAA of both “Head” and “Head + Shoulder”
At high pTa and pT
b, IAA ≈ RAA (inclusive) at head region
arXiv:0801.4545v1[nucl-ex]
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)
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