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Open charm production at RHIC

Open charm production at RHIC. Xin Dong University of Science and Technology of China - USTC. Introduction Charm production in elementary collisions Open charm production in heavy ion collisions Summary and outlook. Thanks to Conference organizers. B. Mueller, nucl-th/0404015.

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Open charm production at RHIC

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  1. Open charm production at RHIC Xin Dong University of Science and Technology of China - USTC • Introduction • Charm production in elementary collisions • Open charm production in heavy ion collisions • Summary and outlook Thanks to Conference organizers

  2. B. Mueller, nucl-th/0404015 Why Charm? – an ideal probe for studying QGP Heavy ! • Charm quarks created at early stage of HIC  total yields scaled by Nbin • Sensitive to the partonic rescatterings • Collectivity, flow?  light flavor thermalization Charm as a probe to test early thermalization! Note: to test the bulk medium response, low pT region are relevant!

  3. Heavy quark has less dE/dx due to suppression of small angle gluon radiation Y. Dokshitzer & D. Kharzeev PLB 519(2001)199 “Dead Cone” effect M. Djordjevic, et. al. PRL 94(2005)112301 J. Adams et. al, PRL 91(2003)072304 B.W. Zhang et. al. PRL 93(2004)072301 N. Armesto et.al.PRD71(2005)054027 R. Rapp et. al. …… h± Charm energy loss Radiative energy loss of heavy quarks and light quarks --- Probe the medium property !

  4. Charm elliptic flow • Coalescence approach • AMPT transport model V. Greco et al., PLB 595(2004)202 B. Zhang et al., nucl-th/0502056 Large X-sec needed to reach high v2 → Charm quark flows → Indication of light flavor thermal equilibrium! Is this large cross section realistic?

  5. The key point is to determine Charm collectivity

  6. Advantages: -- low material budget, clean environ. -- central, forward/backward coverage Advantages: --reconstruction of D mesons -- large acceptance |φ|<2π,|η|<1.5 Charm measurements at RHIC • central arms --- electrons: • DC (tracker),Ring Image Cherenkov (RICH), EMCal • for(back)ward muon arms --- muons: • muon tracker,muon identifier • D recon. from hadronic decay channels: • TPC (+TOF) • electrons: • TPC,TPC+TOF, TPC+EMC

  7. Issue I - total charm cross section • STAR > pQCD • PHENIX >~ pQCD • Charm total cross section is a critical reference for J/ψ suppression/enhancement justification. • Scales (μF and μR ) may be energy dependent. STAR, PRL, 94, 062301 (2005) R. Vogt, private communication

  8. Issue II - pT spectrum PYTHIA curves from S. Kelly, QM04 • PYTHIA spectrum is steeper than data spectrum • beauty contamination: • Typical pQCD calculations: Beauty will take over charm beyond ~4 GeV/c • M. Cacciari et. al. hep-ph/0502203

  9. Centrality dependence of non-photonic electrons in Au + Au QM05 PHENIX, PRL 94, 082301(2005) As expected --- charm quarks are mostly created from initial NN interactions!

  10. M. Djordjevic, et. al. nucl-th/0507019 N. Armesto et. al. private comm. any beauty? Challenges to theoretical friends Current energy loss mechanisms can only account for part of strong suppression of RAA for electrons.

  11. V. Greco et al. PLB 595(2004)202 B. Zhang et al. nucl-th/0502056 Non-photonic electron v2 • Experiments do not agree (2<pT(e)<5 GeV/c)! • v2(e) favors v2(c)=v2(q) at pT(e)<2 GeV/c

  12. If confirmed Summary An exciting heavy flavor program has started at RHIC! • Charm production cross section at 200 GeV measured in elementary collisions. • Total charm yields in HIC approximately obey Nbin scaling. • v2(e) favors non-zero v2(c) !? • RAA(e) ≈ RAA(h) !? Heavy flavor collectivity! Light flavor thermalization! @RHIC Open Issues: pQCD description where is beauty?

  13. Summary Electron approach experiences: 1) spectrum low pT: no distinguishing power high pT: beauty is largely uncertain 2) v2 large statistical and systematical uncertainties • Before any physics conclusion, experimental data must agree! • Single electron approaches are placeholder. • Identified open charm (beauty) measurements are definitely necessary. • The upgrade programs in PHENIX and STAR are essential!

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