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Open charm production at RHIC

Open charm production at RHIC. Xin Dong University of Science and Technology of China - USTC. Outline. Introduction Charm in elementary collisions Open charm production in heavy ion collisions Total charm yields Charm quark Δ E in medium Charm quark v 2 Summary and outlook. ~2.

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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

  2. Outline • Introduction • Charm in elementary collisions • Open charm production in heavy ion collisions • Total charm yields • 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 Charm as a probe to test early thermalization!

  5. 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 !

  6. 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?

  7. The key point is to determine Charm collectivity

  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: • TPC,TPC+TOF, TPC+EMC

  9. 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

  10. Direct charm reconstruction STAR: Mixed-event technique benefiting from large acceptance of the TPC STAR Preliminary A. Tai, QM04 STAR, PRL, 94, 062301 (2005) d+Au 200 GeV

  11. STAR, PRL, 94, 062301 (2005) σcc= 1.4  0.2  0.4 mb EMC -- STAR preliminary Non-photonic electrons STAR:three independent analysis using different sub-detectors PHENIX:three methods to subtract the photonic background p+p 200 GeV S. Kelly, QM04

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

  13. 90% 15% σcc = 1.1  0.1  0.3 mb Spectrum coverage <pT> ~ 1.3 GeV/c The reconstructed D measurement has much smaller systematic uncertainties in determining the total cross section.

  14. 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

  15. Summary on charm in elementary collisions • Open issues of charm production in elementary collisions: • Total charm cross section is higher than typical pQCD calculations! • Spectrum is harder than those from typical PYTHIA predictions! • Beauty contribution Precise measurements of reconstructed open charm in elementary collisions are definitely necessary!

  16. Centrality dependence of non-photonic electrons in Au + Au Centrality dependence of charm production is consistent with Nbin scaling at 0.8<pT(e)<4.0 GeV/c! PHENIX, PRL 94, 082301(2005)

  17. d + Au  Au + Au STAR Highlight talk Approximately Nbin scaling from d+Au to Au+Au! 1.13  0.09  0.42 mb in Au + Au 1.4  0.2  0.4 mb in d + Au As expected --- charm quarks are mostly created from initial NN interactions!

  18. (1) q_hat = 0 GeV2/fm (4) dNg / dy = 1000 (2) q_hat = 4 GeV2/fm (3) q_hat = 14 GeV2/fm RAA of non-photonic electrons PHENIX Highlight talk STAR Highlight talk • Both experiments agree! • Clear evidence of large heavy quark energy loss!

  19. 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.

  20. Charm quark collective motion Electrons: Smearing in pT axis S. Batsouli, et al, Phys.Lett.B 557 (2003) 26 • Electron spectra cannot disentangle different charm hadron shapes at low pT → Need precise measurement of reconstructed D at low pT (<~3GeV/c)!

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

  22. 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?

  23. 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!

  24. 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

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

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