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Xiangli Cui (for the STAR Collaboration)

Di-electron elliptic flow in 2 00 GeV Au+Au collisions at STAR. Xiangli Cui (for the STAR Collaboration). University of Science and Technology of China (USTC) Brookhaven National Laboratory (BNL). Outline. Introduction Electron identification Analysis technique

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Xiangli Cui (for the STAR Collaboration)

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  1. Di-electron elliptic flow in 200 GeV Au+Au collisions at STAR Xiangli Cui (for the STAR Collaboration) University of Science and Technology of China (USTC) Brookhaven National Laboratory (BNL) Xiangli Cui

  2. Outline • Introduction • Electron identification • Analysis technique • Centrality, mass and pT dependence of v2 • Summary Xiangli Cui

  3. Introduction NA60: Eur. Phys. J.C 61(2009) 711-720 R. Rapp, et al .,Phys.Rev. C63 (2001) 054907. Low mass region (Mll <1.1 GeV/c2): In-medium modifications of vector mesons. Chiral symmetry restoration? Intermediate mass region (1.1< Mll <3.0 GeV/c2): QGP thermal radiation. Xiangli Cui

  4. Introduction Rupa Chatterjee , et al., Phys Rev C 75, 054909 (2007) • The mass and pT dependences of di-lepton v2 could give very rich information on specific stages of the fireball expansion • Measurements of v2 of thermal di-lepton could distinguish partonic and hadronic • radiation sources Xiangli Cui

  5. STAR detector • Time Projection Chamber (0<ϕ<2π, |η|<1 ) • Tracking – momentum • Ionization energy loss (dE/dx, PID) • Time Of Flight (0<ϕ<2π, |η|<0.9) • Timing resolution <100ps - significant improvement for PID Xiangli Cui

  6. Electron identification TOF velocity cut to remove slow hadrons • Clean electron PID Au+Au collisions with a combination of TPC dE/dx and TOF velocity • ✓ electron purity ~97% in Au + Au Min Bias collision. • Combine data sets of year 2010 and 2011 ~ 720M Xiangli Cui

  7. Invariant mass distribution Au+Au 0-80%@200GeV efficiency uncorrected efficiency uncorrected pTe>0.2 |ηe|<1 |yee|<1 Background: Like-sign (same) or Unlike-sign (mixed); Signal: Unlike-sign(same) – Background; Signal + Background: Unlike-sign(same) 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. We mix events which are in the same centrality bin (9), vertex z bin (10) and event plane angle bin (100), same magnetic field. Xiangli Cui

  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 ϕ Xiangli Cui

  9. Analysis technique Background: Like-sign (same) or Unlike-sign (mixed). Signal + Background: Unlike-sign(same). Signal: Unlike-sign(same) – Background. v2T : Signal + Background v2, v2B: Background v2, v2S: Signal v2 NS/N(S+B): Signal/(Signal + Background) rj : Resolution of event plane in centrality j <>: average over all di-electron pairs in all events STAR Preliminary Xiangli Cui

  10. Unlike-sign and background v2 Au+Au 0-80%@200GeV In each mass bin: Calculated the v2T, v2Band NS/N(S+B), use above formula to get v2S Background: Mee <=0.7 GeV/c2: Like-sign same event, Mee >0.7 GeV/c2 : Unlike-sign mixed-event Xiangli Cui

  11. Cocktail v2and pT input (Mee<1.1GeV/c2) http://drupal.star.bnl.gov/STAR/files/Bai_Yuting.pdf(Ph.D thesis) Phys. Rev. C 80, 054907 (2009) • components : π0, η, ω, ϕ • Input: flat rapidity (-1,1); • pT: Tsallis function; • φ:1+ 2v2cos(2φ). Phys.Rev. C 79,051901(2009) Xiangli Cui

  12. Cocktail simulation results (Mee<1.1GeV/c2) • 1. Reconstruct e+e- pairs after they decay in the STAR simulators. • 2. Same acceptance cuts applied as in data. • 3.obtain each component v2 and yield. • 4. The cocktail v2 obtained by combining each component v2 (weight by its yield). • 5.The cocktail v2 and each component contribution (weighted by the yield) are shown in the plot. Xiangli Cui

  13. Mee dependence of v2 in Au+Au 200 GeV pTe>0.2 (GeV/c) |ηe|<1, |yee|<1 • Di-electron v2 is consistent with simulation using the measured meson v2 as input in Au+Au at 200 GeV. • Work in progress to include intermediate mass region v2 Xiangli Cui

  14. PT dependence of v2 in Au+Au 200 GeV Au+Au 0-80%@200GeV • Simulated v2 is consistent with measured di-electron v2 within uncertainties in 0-80% Au+Au collisions. • The v2 of di-electrons in the ϕ mass region is consistent with the results of ϕKK within error Xiangli Cui

  15. π0Dalitz decay v2and pTInput in different centralities (Mee<0.14 GeV/c2 ) PHYSICAL REVIEW C 80, 054907 (2009) Phys. Rev. Lett. 97 (2006) 152301 http://arxiv.org/abs/1203.2644v1 • components : π0 • Input: flat rapidity (-1,1); • pT: MT scaling; • φ: 1+2v2cos(2φ). XiangliCui

  16. Centrality dependence of v2 (Mee<0.14 GeV/c2 ) • For each centrality: • 1. Reconstruct e+e- pairs after π0 decay in the STAR simulators. • 2. Same acceptance cuts applied as in data. • 3.obtain e+e- pairs v2 • Di-electron v2 is consistent with simulated results for different centralities in Au+Au at 200 GeV. Xiangli Cui

  17. Summary • For Mee <1.1 GeV/c2, the simulated cocktail v2 are consistent with the measured di-electron v2 • For Mee <0.14 GeV/c2, the simulated e+e- v2 are consistent with the measured di-electron v2 in different centralities. • Work in progress to include intermediate mass region v2 Thanks! Xiangli Cui

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