1Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

Open charm production at RHIC

Xin DongUniversity of Science and Technology of China - USTC

2Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

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

3Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

What we have learned at RHIC

pT (GeV/c)0

~2 ~6

Jet quenchingpQCD at work, high density matter

Hydro at workstrong interactionscollectivity

NCQ groupingpartonic d.o.f

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!

4Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

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!

5Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

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±

6Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

Charm elliptic flow

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

Coalescence approach

Large cross section needed to reach high v2 : Charm quark flows → Indication of light flavor thermal equilibrium! Is the large cross section realistic?

AMPT transport model

B. Zhang et al., nucl-th/0502056

7Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

The key point is to determine

Charm collectivity

8Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

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

9Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

R. Vogt Int. J. Mod. Phys. E 12(2003)211

D mesons

, ’,

Large Q value needed (>≈3GeV)

powerful test for pQCD calculation

Heavy flavor in pQCD

PDFccbar pQCD

10Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

%)8.3(%),68( 00* KDDD s %)8.3(0 KD

Direct charm reconstruction

STAR Preliminary

STAR, PRL, 94, 062301 (2005)

d+Au 200 GeV

STAR: Mixed-event technique benefiting from large acceptance of the TPC

A. Tai, QM04

11Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

Non-photonic electrons

PHENIX: three methods to subtract the photonic background

S. Kelly, QM04

STAR: three independent analysis using different sub-detectors

EMC -- STAR preliminary

σcc = 1.4 0.2 0.4 mbSTAR, PRL, 94, 062301 (2005)

p+p 200 GeV

12Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

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 determination.

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

STAR, PRL, 94, 062301 (2005)

R. Vogt, private communication

13Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

Spectrum coverage

σcc = 1.1 0.1 0.3 mb

The reconstructed D measurement has much smaller systematic uncertainties in determining the total cross section.

<pT> ~ 1.3 GeV/c

90%

15%

14Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

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

15Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

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!

16Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

Centrality dependence of non-photonic electrons in Au + Au

PHENIX, PRL 94, 082301(2005)

Centrality dependence of charm production is consistent with Nbin scaling at 0.8<pT(e)<4.0 GeV/c!

17Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

d + Au Au + Au

STAR Highlight talk

1.13 0.09 0.42 mb in Au + Au

1.4 0.2 0.4 mb in d + Au

Approximately Nbin scaling from d+Au to Au+Au!

As expected --- charm quarks are mostly created from initial NN interactions!

18Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

(3) q_hat = 14 GeV2/fm

(2) q_hat = 4 GeV2/fm

(1) q_hat = 0 GeV2/fm

(4) dNg / dy = 1000

RAA of non-photonic electrons

PHENIX Highlight talk

Both experiments agree! Clear evidence of large heavy quark energy loss!

STAR Highlight talk

19Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

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?

20Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

Charm quark collective motion

Electron spectra cannot disentangle different charm hadron shapes at low pT

→ Need precise measurement of reconstructed D at low pT (<~3GeV/c)!

S. Batsouli, et al, Phys.Lett.B 557 (2003) 26 Electrons: Smearing in pT axis

21Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

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

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.

B. Zhang et al.nucl-th/0502056

22Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

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

23Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

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

24Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

Upgrade detectors at PHENIX

Barrel and Endcap Silicon Vertex Tracker

Direct charm/beauty reconstruction: low pT via e/μ, high pT via Kπ

G. Kunde, WW 05

25Aug. 4-9, 2005, QM2005, Budapest X.Dong, USTC

Upgrade detectors at STAR

Full Barrel MRPC - TOF Heavy Flavor Tracker

Full open charm measurements - direct D-meson V0 reconstruction - spectrum, v2 (low high pT), correlations …

K. Schweda’s talk