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Yifei Zhang University of Science & Technology of China

Charm production at STAR. Yifei Zhang University of Science & Technology of China. 10th Particle Physics Conference April 26-28, Nanjing, China. Thanks to t he conference organizers. Outline. Introductions Signal/Spectra Flow & energy loss Correlations Summary & Outlook.

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Yifei Zhang University of Science & Technology of China

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  1. Charm production at STAR Yifei Zhang University of Science & Technology of China 10th Particle Physics Conference April 26-28, Nanjing, China Thanks to the conference organizers

  2. Outline • Introductions • Signal/Spectra • Flow & energy loss • Correlations • Summary & Outlook Yifei ZhangUSTC

  3. Why measure charm? Mb 4.8 GeV >> Tc, LQCD, Muds Mc 1.3 GeV • Higgs mass: electro-weak symmetry breaking. (current quark mass) • QCD mass: Chiral symmetry breaking. (constituent quark mass) • Heavy quark masses are not modified by QCD vacuum. Strong interactions do not affect them. • Important tool for studying properties of the hot-dense matter created at RHIC energy. Muller nucl-th/0404015 Yifei ZhangUSTC

  4. Charm production cross-section • Charmquarks are believed to be mainly produced at early stage by initial gluon fusions. • Sensitive to initial parton distribution function. • Nuclear and medium properties at initial stage. • Precondition for light flavor thermalization if charm flow.. • Essential for recombination calculations of J/ production. M. Gyulassy & Z. Lin, PRC 51 (1995) 2177 Npart L.Yan, P.Zhuang, N.Xu PRL 97 (2006) 232301 PHENIX data nucl-ex/0611020 Yifei ZhangUSTC

  5. Relativistic Heavy Ion Collider (RHIC)Brookhaven National Laboratory (BNL), Upton, NY Yifei ZhangUSTC

  6. Charm measurements at STAR STAR measurements: • Signal/Spectra D0 K • c   + X (y=0, low pT) • c  e + X • Flow & energy loss Radial flow from NPE RAA from NPE • Correlations e-h, e-D0 Yifei ZhangUSTC

  7. hadronic decay Charm measurement at STAR • Direct D0 reconstruction • muon from charm semileptonic decay • electron from heavy quark semileptonic decay - semileptonic decay • c  e+ + anything (B.R.: 10.3%) • c  + + anything (B.R.: 8.2%) • c  l+ + anything (B.R.: 9.6%) D0  K, B.R.: 3.83% Yifei ZhangUSTC

  8. Outline • Introductions • Signal/Spectra • Flow & energy loss • Correlations • Summary & Outlook Yifei ZhangUSTC

  9. D0 Phys. Rev. Lett. 94 (2005) Direct D-meson reconstructions at STAR STAR Preliminary A. Shabetai QM08 K invariant mass distribution in d+Au, Au+Au minbias, Cu+Cu minbias at 200 GeV collisions. Yifei ZhangUSTC

  10. D0 & Lepton from HF decay at STAR STAR Preliminary New Cu+Cu D0 spectrum agree with Au+Au after number of binary scaled. Low pT muon constrains charm cross-section. Yifei ZhangUSTC

  11. Charm cross-section Total cross-section with large theoretical uncertainty. d+Au: PRL 94 (2005) Cu+Cu:A. Shabetai QM08 Au+Au: Y. Zhang, JPG 32 (2006) S529 Both STAR and PHENIX are self-consistent. STAR results ~ 2 times larger than PHENIX Consistent with NLO calculation. Yifei ZhangUSTC

  12. Outline • Introductions • Signal/Spectra • Flow & energy loss • Correlations • Summary & Outlook Yifei ZhangUSTC

  13. Radial flow – lepton from HF decays D0 STAR Preliminary STAR Preliminary Tfo = 220 MeV (best fit) – freeze out ealier <t> = 0.23 (best fit), <0.42 (1-). favor moderate or small radial flow. -- dense medium, light flavor thermalization. Yifei ZhangUSTC

  14. STAR PRL, 98, 192301 (2007) Charm energy loss, unsolved puzzle No direct D-meson measurement at high pT. Heavy flavor electron suppression was observed in several experiments. Radiative + Collisional eloss calculations describe data better. Question: Partonic eloss mechanism? Bottom contribution? Yifei ZhangUSTC

  15. Outline • Introductions • Signal/Spectra • Flow & energy loss • Correlations • Summary & Outlook Yifei ZhangUSTC

  16. e-h correlations – conical emission Trigger on NPE from heavy quark decays. Section XIII: G. Wang Au+Au 200 GeV Cu+Cu 200 GeV STAR Preliminary Does heavy quark e-loss generate Mach Cone emission? Yifei ZhangUSTC

  17. e-h correlations – bottom contribution (be)/(ce+be) e-h: G. Wang, QM08 e-D0: A. Mischke, QM08 Simulation: ce, be, c+be Extract b/c ratio from the data/simulation comparison Good agreement among different analyses. Data consistent with FONLL. Yifei ZhangUSTC

  18. Does bottom affect charm X-sec? STAR Preliminary Before subtraction: (AuAu MB) (AuAu 0-12%) After bottom contribution subtraction: (AuAu MB) (AuAu 0-12%) Bottom contribution does NOT change charm cross-section (be)/(b+ce) upper limit of NLO is applied Yifei ZhangUSTC

  19. Summary • Charm cross-section is found to follow number of binary collisions scaling. • None zero charm flow is observed at RHIC energy. • Electron suppression is observed at RHIC but the energy loss mechanism is still NOT really understood. • Abounding correlations related to heavy flavor are reported. Yifei ZhangUSTC

  20. Outlook • Currently… • W/o inner tracker, direct measurement of D-mesons through topology reconstruction is impossible due to insufficient track projection resolution close to the collision vertex. Heavy Flavor Tracker • Single muon can not be measured at high pT at STAR. Muon Telescope Detector • Single electron is always suffered from the amount of photonic background. Full barrel Time Of Flight Detector Semileptonic decayed electron is not strongly sensitive to D-mesons. Yifei ZhangUSTC

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