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Xiangli Cui (for the STAR Collaboration)

The elliptic flow of di-electrons in 200 GeV Au+Au from STAR. Xiangli Cui (for the STAR Collaboration). University of Science and Technology of China (USTC) Brookhaven National Laboratory (BNL). Outline Motivation Detector Results of di-electrons v 2 in 200 GeV Au+Au

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Xiangli Cui (for the STAR Collaboration)

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  1. The elliptic flow of di-electrons in 200 GeV Au+Au from STAR Xiangli Cui (for the STAR Collaboration) University of Science and Technology of China (USTC) Brookhaven National Laboratory (BNL) • Outline • Motivation • Detector • Results of di-electrons v2 in 200 GeV Au+Au • Summary and outlook

  2. Motivation I Low mass region (LMR): ✓in-medium modifications of vector mesons Intermediate mass region (IMR): ✓QGP thermal radiation/charm modification STAR preliminary LMR IMR • Di-electrons: Clean probe • no strong interaction - direct information of the medium in heavy ion collisions • probe the whole evolution of the collision

  3. Motivation II • Elliptic 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.

  4. STAR Detector Tracking: TPC Time Projection Chamber 1. Tracking 2. Ionization energy loss (dE/dx PID): 3. Coverage -1<<1 Particle ID: TOF Time Of Flight ---- 1. Timing resolution (<100ps) 2. Coverage: -0.9<<0.9 3. Completed in 2010 (72% in 2009) e STAR preliminary TOF-PID cut: |1/β-1/βexpected|<0.025

  5. Invariant mass distribution STAR preliminary STAR preliminary Mee<=0.7 (GeV/c2 ) : Subtract the like-sign background Mee>0.7 (GeV/c2 ): Subtract the normalized mixed-event background (normalized to like-sign background at Mee(0.7,3)GeV/c2and 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

  6. Unlike-sign and background v2 STAR preliminary STAR preliminary Event-plane method: Signal v2 Unlike-sign v2 Background v2 Signal/(Signal+Background)

  7. v2 versus Mee First di-electrons elliptic flow v2 measured at STAR. Preliminary systematic uncertainties include track quality and PID selections.

  8. Dominant particle contribution in different mass ranges 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 STAR preliminary

  9. v2 of di-electrons from π0 and η Dalitz decay STAR preliminary STAR preliminary PHYSICAL REVIEW C 80, 054907 (2009) 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.

  10. v2 of di-electrons at 0.5<Mee<1.1GeV/c2 STAR preliminary STAR preliminary The elliptic flow of φ->ee is consistent with the result of φ->KK within errors STAR preliminary http://arxiv.org/abs/nucl-ex/0703033v1

  11. 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. Outlook： • Finalize the systematic uncertainties of v2 for di-electrons • A factor of 2 more minimum bias data from run11 200GeV Au+Au collisions

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