1Aug. 10-15, 2005, XXXV ISMD, Czech X.Dong, USTC

Open charm production at RHIC

Xin DongUniversity of Science and Technology of China - USTC

Introduction

Charm production in elementary collisions

Open charm production in heavy ion collisions

Summary and outlook

Thanks toConference organizers

2X.Dong, USTCAug. 10-15, 2005, XXXV ISMD, Czech

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 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!

3X.Dong, USTCAug. 10-15, 2005, XXXV ISMD, Czech

Charm energy loss

k

E

M

dP

k

dkkdCdP Fs

,

)/1()(

0

2220

022

022

22

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±

4X.Dong, USTCAug. 10-15, 2005, XXXV ISMD, Czech

Charm elliptic flow

V. Greco et al., PLB 595(2004)202

Coalescence approach

Large X-sec needed to reach high v2 → 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

5X.Dong, USTCAug. 10-15, 2005, XXXV ISMD, Czech

The key point is to determine

Charm collectivity

6X.Dong, USTCAug. 10-15, 2005, XXXV ISMD, Czech

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,|η|<1.5

7X.Dong, USTCAug. 10-15, 2005, XXXV ISMD, Czech

Issue I - total charm cross section

1) STAR > pQCD PHENIX >~ pQCD

2) Charm total cross section is a critical reference for J/ψ suppression/enhancement justification.

3) Scales (μF and μR ) may be energy dependent.

STAR, PRL, 94, 062301 (2005)

R. Vogt, private communication

8X.Dong, USTCAug. 10-15, 2005, XXXV ISMD, Czech

Issue II - pT 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

9X.Dong, USTCAug. 10-15, 2005, XXXV ISMD, Czech

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

10X.Dong, USTCAug. 10-15, 2005, XXXV ISMD, Czech

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 RAA for electrons.

any beauty?

11X.Dong, USTCAug. 10-15, 2005, XXXV ISMD, Czech

V. Greco et al.PLB 595(2004)202

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

B. Zhang et al.nucl-th/0502056

12X.Dong, USTCAug. 10-15, 2005, XXXV ISMD, Czech

Summary

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) !?

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

13X.Dong, USTCAug. 10-15, 2005, XXXV ISMD, Czech

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 pT: no distinguishing power high pT: beauty is largely uncertain 2) v2

large statistical and systematical uncertainties