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Di-lepton production at STAR

Di-lepton production at STAR. L ijuan Ruan for the STAR Collaboration ( Brookhaven National Laboratory ). Outline: Motivation and Introduction Recent results from STAR Future perspectives from STAR Conclusions and outlook. S. Bass. Probe the medium properties.

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Di-lepton production at STAR

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  1. Di-lepton production at STAR LijuanRuan for the STAR Collaboration (Brookhaven National Laboratory) Outline: • Motivation and Introduction • Recent results from STAR • Future perspectives from STAR • Conclusions and outlook Moriond QCD and High Energy Interactions, Mar. 10-17

  2. S. Bass Probe the medium properties • H. van Hees and R. Rapp, Nucl.Phys.A806 (2008) 339; T. Renk and J. Ruppert, PRC77(2008)024907 • In medium modification of vector mesons and thermal radiation: di-lepton continuum NA60, PRL100,022302(2008) NA60, Eur.Phys.J.C59,607(2009) Moriond QCD and High Energy Interactions, Mar. 10-17

  3. STAR detector: TPC & MRPC-TOF • A recent technology (TOF) ---- • Multi-gap Resistive Plate Chamber • adopted from CERN-ALICE. • Good timing resolution, • (, K) < 1.6 GeV/c, proton < 3 GeV/c • Coverage: -0.9<<0.9 • Coverage • (4% y2008, 72% y2009, 100% y2010) Time Projection Chamber • Tracking • Ionization energy loss (dE/dx): • (, K) < 0.7 or > 3 GeV/c, • proton < 1 or > 3 GeV/c • Coverage -1<<1 Moriond QCD and High Energy Interactions, Mar. 10-17

  4. STAR Time of Flight detector performance |1/-1|<0.03 STAR, PLB616(2005)8 STAR, PRL94(2005)062301 200 GeV d+Au collisions 200 GeV d+Au collisions TOF PID: (, K) ~ 1.6, proton ~ 3 GeV/c STAR Collaboration, PLB616(2005)8 TOF enables clean electron PID up to PT < 3 GeV/c. STAR Collaboration, PRL94(2005)062301 M. Shao et al., NIMA 558(2006)419 Moriond QCD and High Energy Interactions, Mar. 10-17

  5. Di-electron signal Di-electon signal: e+e- pairs from light flavor meson and heavy flavor decays (charmonia and open charm correlation): Pseudoscalar meson Dalitz decay: 0 , η, η' e+e- Vector meson decays:0 , ,  e+e-,  0 e+e- , ηe+e- Heavy flavor decays: J/e+e- , ccbar e+e- X, bbbar e+e- Drell-Yan contribution In Au+Au collisions, we search for QGP thermal radiation at 1.1<Mee<3.0 GeV/c2(intermediate mass range) Vector meson in-medium modificationsat Mee<1.1 GeV/c2(low mass range) Moriond QCD and High Energy Interactions, Mar. 10-17

  6. Di-lepton production in 200 GeV p+p cocktail simulation is consistent with di-electron spectrum in p+p collisions at 200 GeV charm correlation contribution dominates in the intermediate mass region (1.1-2.9 GeV/c2) Simulation: charm correlation contribution is from PYTHIA .   J/ STAR acceptance: |yee|<1, |ηe|<1, pT>0.2 GeV/c STAR, QM2011,SQM2011 Moriond QCD and High Energy Interactions, Mar. 10-17

  7. Di-lepton spectra in 200 GeV Au+Au 0-80%Au+Au 0-10%Au+Au     J/ J/ possible enhancement factor in 0.15<Mee<0.75 Gev/c2 STAR, QM2011, SQM2011 PHENIX results, see K. Okada’s talk. Moriond QCD and High Energy Interactions, Mar. 10-17

  8. ee spectra in 200 GeV p+p and Au+Au • ωee measurements via • di-lepton channel in p+p and • Au+Au at STAR • ωee flow pattern is similar to • light hadrons STAR Preliminary Tsallis Blast-wave(TBW) fit: <β>=0 in p+p, <β>=0.47 in 0-80% AuAu. Z.Tang et al., arXiv:1101.1912 STAR, QM2011, SQM2011 Moriond QCD and High Energy Interactions, Mar. 10-17

  9. ee spectra in 200 GeV Au+Au • The invariant yield of  via • di-lepton channel in Au+Au is • consistent with that from • hadronic decay channel. • mass and width between data • and simulation: consistent STAR Preliminary STAR, SQM2011 Moriond QCD and High Energy Interactions, Mar. 10-17

  10. v2 versus Mee at 200 GeV Au+Au STAR Preliminary Di-electron v2 versus pT & Mee: probe the properties of the medium from hadron-gas dominated to QGP dominated constrain QGP dynamics (η/s, T, t0…) A factor of 2 more minbias data from run11 is on disk. STAR, SQM2011, DNP2011 Moriond QCD and High Energy Interactions, Mar. 10-17

  11. v2 of di-electrons from π0 and η Dalitz decay STAR Preliminary STAR Preliminary PRC 80, 054907 (2009) To provide a comparison (blue) curve from simulation: 1. Parameterize  meson v2 results 2. Do the Dalitz decay simulation and obtain expected v2 of di-electrons pairs from 0 Dalitz decay. 3. This is consistent with our di-electrons v2 results. • To provide a comparison (blue) curve from simulation: • Assume η v2 same as KS • do the same Dalitz decay • procedure STAR, SQM2011, DNP2011 Moriond QCD and High Energy Interactions, Mar. 10-17

  12. Measure charm correlation with MTD upgrade: ccbare+m Z. Xu, BNL LDRD 07-007; L. Ruan et al., JPG36 (2009) 095001 R. Rapp, hep-ph/0010101 e correlation simulation with Muon Telescope Detector (MTD) at STAR from ccbar:S/B=2 (Meu>3 GeV/c2 and pT(e)<2 GeV/c) S/B=8 with electron pairing and tof association MTD: construction starts in FY2011; project completion in FY2014 Moriond QCD and High Energy Interactions, Mar. 10-17

  13. Di-lepton measurements at STAR Moriond QCD and High Energy Interactions, Mar. 10-17

  14. Summary STAR has started the di-lepton program with a bright future enabled by the TOF upgrade : • Di-lepton spectrum in 200 GeV p+p collisions: Cocktail simulation consistent with data Charm correlation contribution dominates at intermediate mass • Di-lepton in 200 GeV Au+Au collisions: A possible low mass enhancement with respect to cocktail expectation at Mee 0.15-0.75 GeV/c2 ee shows a similar flow velocity at freeze-out as light hadrons  yields are similar between di-leptonic decay and hadronic decay channel Di-lepton v2 from low to high mass measured Towards the future: Differential measurements (Mee, pT, v2) are on-going Energy dependence (19-200 GeV) can be systematically studied at STAR e-µ correlation (spectrum and v2) to distinguish heavy flavor production from initial lepton pair production with MTD upgrade Moriond QCD and High Energy Interactions, Mar. 10-17

  15. Backup Moriond QCD and High Energy Interactions, Mar. 10-17

  16. Compared to theoretical calculations within STAR acceptance HG_med, QGP from R. Rapp (private communication) R. Rapp and J.Wambach, Adv. Nucl. Phys. 25, 1 (2000). Blue dotted: HG_medium Pink dotted: QGP Solid lines: upper: cocktail + HG+QGP lower: cocktail Moriond QCD and High Energy Interactions, Mar. 10-17

  17. v2 of di-electrons at 0.5<Mee<1.1 GeV/c2 STAR preliminary STAR preliminary The elliptic flow of ee is consistent with the result of KK within errors STAR preliminary KK: PRL99(2007)112301 STAR, DNP2011 Moriond QCD and High Energy Interactions, Mar. 10-17

  18. The most recent quarkonium results STAR, QM2011, SQM2011 • J/ψ RAA increase from low to high pT • Not suppressed in peripheral Au+Au but suppressed in central Au+Au at high pT • No significant v2 • Upsilon suppressed in Au+Au Moriond QCD and High Energy Interactions, Mar. 10-17

  19. Data sets for di-electron analyses large acceptance of the TOF system and low material budget * at mid-rapidity * beam pipe (0.29% radiation length), beam pipe wrap (0.14%), air (0.17%), IFC (0.45%) Moriond QCD and High Energy Interactions, Mar. 10-17

  20. Electron identification capability 200 GeV p+p collisions |1/β-1|<0.03 |1/β-1/βexpected|<0.025 Clean electron identification obtained with TPC+TOF: Electron purity: 99% in p+p and 97% in minbias Au+Au Hadron contamination contribution to di-lepton is insignificant and taken as part of systematic uncertainties. Moriond QCD and High Energy Interactions, Mar. 10-17

  21. Di-electron signals in p+p and Au+Au STAR preliminary p+p @ 200 GeV Moriond QCD and High Energy Interactions, Mar. 10-17

  22. Di-lepton background Mixed-event normalized to like-sign within 0.4 - 1.5 GeV/c2 Cross-pair bg. can only be described by like-sign method. For minimum bias events, we subtracted like-sign bg at Mee<0.7 GeV/c2, mixed-event bg subtraction was applied at Mee>0.7 GeV/c2. Moriond QCD and High Energy Interactions, Mar. 10-17

  23. Di-lepton azimuthal angle distribution STAR preliminary STAR preliminary Mixed-event normalized to like-sign within 0.4 - 1.5 GeV/c2 Cross-pair bg. can only be described by like-sign method. For minimum bias events, we subtracted like-sign bg at Mee<0.7 GeV/c2, mixed-event bg subtraction was applied at Mee>0.7 GeV/c2. Moriond QCD and High Energy Interactions, Mar. 10-17

  24. Di-lepton background Mixed-event normalized to like-sign within 1 - 3 GeV/c2 Cross-pair bg. can only be described by like-sign method. For minimum bias events, we subtracted like-sign bg at Mee<0.7 GeV/c2, mixed-event bg subtraction was applied at Mee>0.7 GeV/c2. Moriond QCD and High Energy Interactions, Mar. 10-17

  25. Low mass enhancement PHENIX PRC 81 (2010) 034911 Enhancement factor in 0.15<Mee<0.75 Gev/c2 Note: Acceptance difference etc. Moriond QCD and High Energy Interactions, Mar. 10-17

  26. Systematic uncertainties p+p: Au+Au: STAR preliminary STAR preliminary Moriond QCD and High Energy Interactions, Mar. 10-17

  27. Reproduce PHENIX cocktail • Reproduce the cocktail within PHENIX acceptance by our method. • The momentum resolution are still from STAR. STAR preliminary Scaled by all the yields from PHENIX paper[1], we can reproduce the PHENIX cocktail. [1]. Phys. Rev. C 81, 034911 (2010). Moriond QCD and High Energy Interactions, Mar. 10-17

  28. Check with acceptance difference STAR preliminary STAR preliminary Acceptance difference: Scaled by the acceptance difference Scaled by same meson and charm yields. Difference at low mass is not from the simulation but from the measurements. Moriond QCD and High Energy Interactions, Mar. 10-17

  29. v2 standard event-plane method ν2Total is flow of unlike-sign pairs. v2B(M) is flow of background calculated using the like-sign or mixed events pairs. v2S is flow of signal. NS is the signal number, NB is the background (like-sign) number. N(S+B) is unlike-sign number. Moriond QCD and High Energy Interactions, Mar. 10-17

  30. Unlike-sign and background v2 STAR preliminary STAR preliminary Signal flow Unlike-sign v2 Background v2 Signal/(Signal+Background) Moriond QCD and High Energy Interactions, Mar. 10-17

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