1. Aug. 10-15, 2005, XXXV ISMD, Czech X.Dong, USTC 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. X.Dong, USTC Aug. 10-15, 2005, XXXV ISMD, Czech 2 Why Charm? – an ideal probe for studying QGP B. Mueller, nucl-th/0404015 Heavy !  Charm quarks created at early stage of HIC  total yields scaled by N bin  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 p T region are relevant!

3. X.Dong, USTC Aug. 10-15, 2005, XXXV ISMD, Czech 3 Charm energy loss Y. Dokshitzer & D. Kharzeev PLB 519(2001)199 Radiative energy loss of heavy quarks and light quarks --- Probe the medium property ! Heavy quark has less dE/dx due to suppression of small angle gluon radiation “Dead Cone” effect M. Djordjevic, et. al. PRL 94(2005)112301 B.W. Zhang et. al. PRL 93(2004)072301 N. Armesto et. al. PRD71(2005)054027 R. Rapp et. al. …… J. Adams et. al, PRL 91(2003)072304 h±h±

4. X.Dong, USTC Aug. 10-15, 2005, XXXV ISMD, Czech 4 Charm elliptic flow V. Greco et al., PLB 595(2004)202 Coalescence approach Large X-sec needed to reach high v 2 → Charm quark flows → Indication of light flavor thermal equilibrium! Is this large cross section realistic? AMPT transport model B. Zhang et al., nucl-th/0502056

5. X.Dong, USTC Aug. 10-15, 2005, XXXV ISMD, Czech 5 The key point is to determine Charm collectivity

6. X.Dong, USTC Aug. 10-15, 2005, XXXV ISMD, Czech 6 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 Advantages: -- low material budget, clean environ. -- central, forward/backward coverage Advantages: -- reconstruction of D mesons -- large acceptance |φ|<2π,|  |<1.5

7. X.Dong, USTC Aug. 10-15, 2005, XXXV ISMD, Czech 7 Issue I - total charm cross section 1)STAR > pQCD PHENIX >~ pQCD 2)Charm total cross section is a critical reference for J/ψ suppression/enhance ment justification. 3)Scales (μ F and μ R ) may be energy dependent. STAR, PRL, 94, 062301 (2005) R. Vogt, private communication

8. X.Dong, USTC Aug. 10-15, 2005, XXXV ISMD, Czech 8 Issue II - p T spectrum  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 PYTHIA curves from S. Kelly, QM04

9. X.Dong, USTC Aug. 10-15, 2005, XXXV ISMD, Czech 9 Centrality dependence of non-photonic electrons in Au + Au PHENIX, PRL 94, 082301(2005) As expected --- charm quarks are mostly created from initial NN interactions! QM05

10. X.Dong, USTC Aug. 10-15, 2005, XXXV ISMD, Czech 10 Challenges to theoretical friends M. Djordjevic, et. al. nucl-th/0507019 N. Armesto et. al. private comm. Current energy loss mechanisms can only account for part of strong suppression of R AA for electrons. any beauty?

11. X.Dong, USTC Aug. 10-15, 2005, XXXV ISMD, Czech 11 V. Greco et al. PLB 595(2004)202 Non-photonic electron v 2  Experiments do not agree (2<p T (e)<5 GeV/c)!  v 2 (e) favors v 2 (c)=v 2 (q) at p T (e)<2 GeV/c B. Zhang et al. nucl-th/0502056

12. X.Dong, USTC Aug. 10-15, 2005, XXXV ISMD, Czech 12 Summary  Charm production cross section at 200 GeV measured in elementary collisions.  Total charm yields in HIC approximately obey N bin scaling.  v 2 (e) favors non-zero v 2 (c) !?  R AA (e) ≈ R AA (h) !? An exciting heavy flavor program has started at RHIC! Open Issues: pQCD description where is beauty? Heavy flavor collectivity! Light flavor thermalization! @RHIC If confirmed

13. X.Dong, USTC Aug. 10-15, 2005, XXXV ISMD, Czech 13 Summary  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! Electron approach experiences: 1) spectrum low p T : no distinguishing power high p T : beauty is largely uncertain 2) v 2 large statistical and systematical uncertainties