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Yifei Zhang University of Science & Technology of China

Explore the production and measurements of charm particles at the 10th Particle Physics Conference. Discuss the importance of charm in studying dense matter and symmetries in physics. Highlight results from RHIC and ongoing studies on charm properties and energy loss.

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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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