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Xiangli Cui (for the STAR Collaboration)

The elliptic flow of di-electrons in 200 GeV Au+Au from STAR

OutlineMotivationDetectorResults of di-electrons v2 in 200 GeV Au+AuSummary and outlook

University of Science and Technology of China (USTC)Brookhaven National Laboratory (BNL)

Motivation I

LMR IMRDi-electrons: Clean probe no strong interaction - direct information of the medium in heavy ion collisionsprobe the whole evolution of the collision

Low mass region (LMR):✓in-medium modifications ofvector mesons

Intermediate mass region (IMR):✓ QGP thermal radiation/charm modification

STAR preliminary

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Motivation IIElliptic flow, caused by anisotropic pressure gradient, sensitive to early time in the system evolution.

Different particle species dominate in different mass ranges.

study the Integral flow for the dominant particle at a certain mass

In different mass ranges, study the particle flow versus pT.

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Time Projection Chamber 1. Tracking2. Ionization energy loss (dE/dx PID): 3. Coverage -1<<1

Time Of Flight ----1. Timing resolution (<100ps)2. Coverage: -0.9<<0.93. Completed in 2010 (72% in 2009)

Particle ID: TOF

Tracking: TPC

TOF-PID cut: |1/β-1/βexpected|<0.025

STAR Detector

e

STAR preliminary

Invariant mass distribution

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Mee<=0.7 (GeV/c2 ) : Subtract the like-sign backgroundMee>0.7 (GeV/c2 ): Subtract the normalized mixed-event background (normalized to like-sign background at Mee(0.7,3)GeV/c2 and pT (0,4)GeV/c )

Mee range(GeV/c2) :0.-0.14, 0.14-0.3, 0.3-0.5, 0.5-0.7,0.7-0.9, 0.9-1.1, 1.1-2.9, 2.9-3.3

STAR preliminarySTAR preliminary

Unlike-sign and background v2

)(*))(1(*)()()(

2)(

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NvM

N

NsMvMv

BS

SS

BS

BTotal

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Unlike-sign v2 Background v2 Signal/(Signal+Background)

Signal v2

STAR preliminarySTAR preliminary

Event-plane method:

v2 versus Mee

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First di-electrons elliptic flow v2 measured at STAR.

Preliminary systematic uncertainties include track quality and PID selections.

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Dominant particle contribution in different mass ranges

STAR preliminary Mee(0-0.14) : π0+others

Mee(0.14,0.3): η+others

Mee(0.5,0.7) : charm+ρ+ others

Mee(0.7,0.9): ω+others

Mee(0.9,1.1): φ+others

Mee(1.1,2.9): charm+other

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1. Parameterize π meson v2 results 2. Do the Dalitz decay simulation and obtain expected v2 of di-electrons pairs from π0 Dalitz decay. 3. This is consistent with our di-electrons v2 results.

Assume η v2 same as do the same Dalitz decay procedure.

v2 of di-electrons from π0 and η Dalitz decay

0SK

STAR preliminary

STAR preliminary

PHYSICAL REVIEW C 80, 054907 (2009)

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The elliptic flow of φ->ee is consistent with the result of φ->KK within errors

v2 of di-electrons at 0.5<Mee<1.1GeV/c2

STAR preliminary

STAR preliminary

STAR preliminary

http://arxiv.org/abs/nucl-ex/0703033v1

Summary ： • Report preliminary results of di-electrons v2 versus mass and v2

versus pT in different mass range in Au+Au 200GeV.

• v2 of di-electrons from π0 Dalitz decays is consistent with expectations from the measured v2 of PHENIX π0 and STAR π+ + π-.

• The v2 of φ->ee is consistent with results of φ->KK.• Preliminary systematic uncertainties include the track quality and

PID selections.

• Finalize the systematic uncertainties of v2 for di-electrons

•A factor of 2 more minimum bias data from run11 200GeV Au+Au collisions

Outlook：

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