Open charm production at RHIC

1. Open charm production at RHIC Xin Dong University of Science and Technology of China - USTC Many Thanks to: H. Huang, H. Ritter, K. Schweda, P. Sorensen, A. Tai, N. Xu, Z. Xu, H. Zhang, Y. Zhang M. Djordjevic, L. Grandchamp, M. Gyulassy, J. Raufeisen, R. Vogt, X.-N. Wang

2. Outline • Introduction • Open charm production in heavy ion collisions • Charm production cross section • Charm collective motion • Charm quark ΔE in medium • Charm quark v2 • Summary and outlook

3. ~2 ~6 pT (GeV/c) 0 What we have learned at RHIC NCQ grouping partonic d.o.f Jet quenching pQCD at work, high density matter Hydro at work strong interactions collectivity • Jet-quenching: high density medium created • Large v2 and βT: partonic collectivity • NCQ-grouping: partonic collectivity and deconfinement To fix the partonic EOS, one must test the thermalization experimentally. Heavy flavor probe: Heavy flavor collectivity → light flavor thermalization Note: to test the bulk medium response, low pT region is relevant!

4. 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

5. D mesons Large Q value needed (>≈3GeV) powerful test for pQCD calculation , Y’, c R. Vogt Int. J. Mod. Phys. E 12(2003)211 PDF pQCD ccbar Heavy flavor in pQCD

6. 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 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 M. Djordjevic, et. al. PRL 94(2005)112301 Energy loss of heavy quarks and light quarks --- Probe the medium property the nature of parton interaction !

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

8. 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, muons: • TPC,TPC+TOF, TPC+EMC

9. Charm production cross section Y.F. Zhang (STAR), SQM06 PHENIX, PRL 94, 082301(2005) Centrality dependence of charm production is consistent with Nbin scaling at 0.8<pT(e)<4.0 GeV/c! 1)Charm from hadronic channel 2)Charm from muon at very low pT 3)Charm from electrons

10. d + Au  Au + Au H. Zhang (STAR) QM05 Approximately Nbin scaling from d+Au to Au+Au! 1) charm quarks are mostly created from initial NN interactions! 2) Systematic difference between PHENIX and STAR

11. Closed charm suppression/enhancement ? T. Matsui and H. Satz, PLB 178, 416(1996). L. Grandchamp and R. Rapp, PLB523 , 60(01). A. Andronic, et al., PLB571 , 36(03). RHIC RHIC Precise centrality dependence measurements on charm production cross section are important! • direct pQCD production • medium effect (chiral) • absorption (normal, color screening)

12. open-charm hadron AuAu Central , K, p Charm collective motion Y.F. Zhang (STAR), SQM06 STAR Preliminary Power-law and Blast Wave charm decay D0 + e fit in d+Au collisions. D0 +  + e fit in minbias Au+Au collisions.  + e fit in central Au+Au collisions. Expected to freeze out earlier –T > 140 MeV Collective velocity – charm flow? <T> < , 

13. Challenge to radiative energy loss Radiative energy loss mechanisms can only account for part of strong suppression of RAA for electrons.

14. New energy loss mechanism Elastic collision energy loss becomes important at S. Wicks et al., nucl-th/0512076 • Inclusion of elastic collision energy loss • Jet path length fluctuation

15. B.R. (6.87±0.28)% Au+Au 0-10% B.R. (17.2±1.9)% B.R. (4.5±1.7)% p+p Charm baryon contribution STAR QM05 P. Sorensen et al. nucl-th/0512042

16. Non-photonic electron v2 • v2(e) favors non-zero v2(c) at pT(e)<2 GeV/c.

17. v2 and RAA S. Sakai (PHENIX), RHIC Users Mtg • RAA ~ 1.0 @ peripheral collision but v2 still non-zero • indicate charm quarks interact with medium not only central but also peripheral

18. Achievements Open issues Charm production cross sections in p+p, d+Au and AuAu Measured X-sec > pQCD Systematic difference between PHENIX and STAR Large uncertainties Finite collective velocity High freeze-out temperature Beauty’s contribution Strong suppression of non-photonic electron spectrum in central AuAu Charm thermal motion Nature of parton interacting with medium Light flavor thermalization Finite v2 of non-photonic electrons in AuAu Summary Much more precise measurements on heavy flavor are called for !

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

20. Correlations between electrons and D, B The correlation between the decayed electrons and heavy-flavor hadrons is weak.

21. Upgrade detectors at PHENIX Barrel and Endcap Silicon Vertex Tracker G. Kunde, WW 05 • Direct charm/beauty reconstruction: • low pT via e/μ, high pT via Kπ

22. Upgrade detectors at STAR Full Barrel MRPC - TOF Heavy Flavor Tracker K. Schweda QM05 • Full open charm measurements - direct D-meson V0 reconstruction - spectrum, v2 (low  high pT), correlations …