Study jet energy loss with 2 particle correlations
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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. 0-20% Au+Au20-40%60-92%.

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Study Jet Energy Loss with 2-particle Correlations

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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

  • 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


We know jet quenches in aa relative to p p and we measure per trigger yield

0-20% Au+Au20-40%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

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Hua Pei of ISU for PHENIX at QM08


A jet function can be divided into regions

A Jet Function Can Be Divided into Regions

arXiv:0801.4545v1

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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


We measure the central au au jet spectrum at head region and compare to p p

We Measure the Central Au+Au Jet Spectrum at Head Region and Compare to p+p

arXiv:0801.4545v1

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Each panel shows a different pTa (trigger), and plotted as function of pTb (assoc)

Hua Pei of ISU for PHENIX at QM08


We use i aa to quantify the change of jet spectrum

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


The modification of per trigger yield i aa has strong assoc p t dependence

The Modification of per-trigger Yield (IAA) has strong assoc pT Dependence

arXiv:0801.4545v1

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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


Compare jet spectrum mean pt of head region to inclusive spectrum

Compare Jet Spectrum (mean pT) of Head Region to Inclusive Spectrum

arXiv:0801.4545v1

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“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


J aa is used to measure the change of particle pairs induced by di jet

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


J aa pair suppression

JAA pair suppression

arXiv:0801.4545v1

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  • 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


Relative energy loss back to back jet

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


The spectrum is fitted to get x h

^

The spectrum is fitted to get xh

Hua Pei of ISU for PHENIX at QM08


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

Compare Au+Au x to p+p x

Shown by Michael J. Tannenbaum DNP07

Hua Pei of ISU for PHENIX at QM08


Change the surface bias of near side

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


This 2 1 changes near side jets of both p p and cu cu

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


Centrality dependence of near side yields

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


Another handle on path length reaction plane dependence

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


Conclusion

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


Back up

Back up

Hua Pei of ISU for PHENIX at QM08


The modification of per trigger yield i aa has strong assoc p t dependence1

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


The iaa of both head and head shoulder

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


The mean pt as a function of pt b range

The mean pT as a function of pTB range

arXiv:0801.4545v1

[nucl-ex]

Hua Pei of ISU for PHENIX at QM08


Source of formula on x h

Source of formula on xh

PHYSICAL REVIEW D 74, 072002 (2006)

Hua Pei of ISU for PHENIX at QM08


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