open charm measurements from star

Feb. 2nd, 05, LANL X.Dong, USTC/LBNL 1

Open Charm Measurements from STAR

Xin Dong University of Science & Technology of China

Lawrence Berkeley National Laboratory

H. Huang, H. Ritter, L. Ruan, K. Schweda, P. Sorensen, A. Tai, N. Xu, Z. Xu, H. Zhang

L. Grandchamp, J. Raufeisen, R. Vogt

Many Thanks to Dr. Gerd Kunde!

X.Dong, USTC/LBNL 2Feb. 2nd, 05, LANL

Outline

Introduction & Motivation

Direct charm reconstruction

Indirect electron measurements

Discussions

Conclusions & outlook


Heavy flavor in pQCD

D mesons

, ’,

Large Q value needed (>≈3GeV)

pQCD should work better!

π0 measurements are consistent with NLO pQCD calculation!

Charm should be better!!

PHENIX, PRL 91, 241803(2003) STAR, PRL 92, 171801(2004)


(p)QCD Test

Total cross section measurement --- not depend on the fragmentation models A powerful test of QCD calculations !

Charm spectrum measurement --- fragmentation test for theory predictions.


Heavy flavors – a unique probe to QGP

J/D

K*

K

p

d

TT

saturatessaturates

Q2

time

Charm quark mostly produced from the initial fusion of partons (mostly gluons)

Z. Lin & M. Gyulassy, PRC 51 (1995) 2177

sensitive to Initial Nuclear Effects

Z. Lin & M. Gyulassy, PRL 77 (1996) 1222

dN

/dM

dy

rati

o (S

h/n

o S

h)


Heavy quark energy loss

M. Djordevic & M. Gyulassy QM04, nucl-th/0404006

● Heavy Quark has less dE/dx due to suppression of small angle gluon radiation

k

E

M

dP

k

dkkdCdP Fs

,

)/1()(

0

2220

022

022

22

Y. Dokshitzer &D. Kharzeev PLB 519(2001)199

J. Adams et. al, PRL 91(2003)072304


J/ψ production: suppression/enhancement?

J/ψ suppression scenario in QGP ! --- Debye screening

A. Andronic et. al. PLB 571,36(2003)

Statistical model: Large ccbar yield in one heavy ion collision recombination production J/ψ possible J/ψ enhancement

Statistical model

Total charm yield from pQCD calculations!


Charm quark flow

Charm quark flows -> Strong indication of thermalization of light quarks

V. Greco, C.M. Ko, R. Rapp, PLB 595(2004)202 Coalescence approach


Single electrons Open charm v2

X. Dong et. al, PLB597, 328(2004).

At pT > 2.5 GeV/c:

1) D-meson spectrum is ‘hard’, yields of pion will be small, measure D-decayed electron to infer the open charm v2

2) D-meson flow indication of light flavor thermal equilibrium.


Previous Experiments

Low-energy fixed target – direct D measurement

Fermilab E769, PRL 77, 2388 (1996)

ISR 52-63GeV – inconsistency, S.P.K. Tavernier Rep. Prog. Phys. 50, 1439 (1987)UA2: 630 GeV p+pbar (two electron data points), O. Botner et al. PLB 236 (1990) 488

CDF directy D measurement -- high pT

CDF, PRL 91, 241804 (2003)


Measurements in heavy ion collisions

PHENIX Au+Au@130GeV Phys. Rev. Lett. 88, 192303 (2002)

Nbin scaling for open charm spectrum Total cross section consistent with NLO pQCD calculation


STAR detector

MagnetMagnet

CoilsCoils

Central Central TriggerTriggerBarrel Barrel (CTB)(CTB)

ZCalZCal

Time Time Projection Projection

ChamberChamber(TPC)(TPC)

Year 2000Year 2000

Barrel EM Cal Barrel EM Cal (BEMC)(BEMC)

Silicon Vertex Silicon Vertex Tracker (SVT)Tracker (SVT)Silicon Strip Silicon Strip Detector (SSD)Detector (SSD)

FTPCFTPCEndcap EM CalEndcap EM CalFPDFPD

TOFp, TOFrTOFp, TOFr

Year 2001+Year 2001+


D0 direct reconstruction

Event mixing technique

KD0 ( Br. 3.83%)

First Direct Open CharmReconstruction at RHIC

STAR PRL, in print


%)2.9(KD

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

%)2.6)((00 KD

%)8.3(0 KD

D mesons measured at STAR

STAR Preliminary


Open charm spectrum

STAR Preliminary

1) D*/D0 ratio is consistent with other experiments and models2) Power-law describes the spectrum well up to ~11GeV/c


Hadron identification: STAR Collaboration, nucl-ex/0309012

Indirect measurement D→e+X

STAR PRL, in print

electrons

Electron identification: TOFr |1/ß-1| < 0.03 TPC dE/dx electrons!!!


Inclusive electrons

1. With TOF and dEdx, electrons can be identified well from ~0.3GeV/c up to ~3GeV/c!

2. Select electrons (e-) using dE/dx only (2-4GeV)

Hadron contamination was corrected for ~ 5-30% pT 2-4 GeV/c

STAR Preliminary


Measurements of electron background

Background Topology:• TOFr tagged e+/e-

• Large TPC acceptance• High efficiency of reconstructing electron pair

TPC

For the γ conversion and π0 Dalitz decay, background spectra are obtained from data using kinematical selection of the pairs in TPC

γ conversionπ0 , η Dalitz decaysKaon decaysρ ω Φ vector meson decaysheavy quark semi-leptonic decayothers

Single ElectronsSpectra

γ conversion and π0 Dalitz decays are the dominant sources at low pt region.

background

signal


Background subtraction

a) Data: background spectrakinematical selection of the conversion and 0 Dalitz decay pairs in TPC

b) MC: conversion and 0 Dalitz decay reconstruction efficiency ~60%

c) MCMC: relative contributions of different sources: determined from PYTHIA/HIJING

+ detector simulations

conversion and 0 Dalitz decay reconstruction efficiency :~60% at pT>1.0 GeV/c

Invariant Mass Square

Rejected

Signal

STAR Preliminary

STAR Preliminary


Background contribution

An increasing excess found at higher pT region, pT > 1.0 GeV/c, → expected to be contribution of semileptonic decay from heavy flavor hadrons

STAR PRL, in print


Combining fit

1) Good agreement between D0 and electrons spectra2) d+Au and p+p do not show significant nuclear effect

STA

R P

RL,

in p

rint

Combined fit forD0 and electrons

PYTHIA: MSEL = 1, CTEQ5M1


Charm yields

Assumption for the combining fit: 1. D0 spectrum follows the power law function 2. only normalization scale between different D meson pT spectrum 3. All the background subtracted electrons are from D decay

p+p and d+Au electron spectra show approximately binary scaling

.)(3.0.)(3.03.1 sysstatRedAu 1<pT<4GeV/c


Charm production at mid-rapidity

Color Dipole: Phys. Rev. D67 (2003) 054008

R.Vogt, A. Tai, private communicationsHSD: Phys. Rev. C67 (2003) 054905

STAR Preliminary


Charm total cross-section

1) NLO pQCD calculations under predict the total charm production cross section at RHIC

2) Scales (muR or muF) may be energy dependent

Mid-rapidity → Full rapidity 4.7 ± 0.7

STAR PRL, in print


J/ψ production

PHENIX J/psi in AuAu, PRC 69 (2004) 014901

This upper limit invalidates the expectation from large open charm cross section!

1) Statistical model prediction implies possible J/psi enhancement

2) But with STAR ccbar cross section (from d+Au) , a much larger enhancement (~3-10) for J/psi production in central Au+Au collisions.


Directly reconstructed D mesons

D and electron spectra are consistent!

Electrons from D decay

Consistency check

STAR PreliminarySTAR Preliminary


Open charm spectrum is harder !

Phenix: PRL. 88, 92303(2002)

D. Kharzeev, hep-ph/0310358

D0, D*, D

A. Tai, A. Suaide, QM04STAR Preliminary

B decay dominated region

STAR Preliminary


Charm quark hadronization at RHIC

bare c-quark spectrum, normalized to measured dn/dy

MRST HO

Peterson’s function ε=0.06

c quark

=4,3,2,1 (GeV)^22Tk

After broadening and fragmentation

Tk

A. Tai QM04

STAR Preliminary

R. Vogt, hep-ph/0203151

1) Higher order processes needed2) Charm hadronization through fragmentation + recombination?


Non-photonic electron v2

STAR: 0-80% (F.Laue SQM04) PHENIX: Minimum bias statistical error only HSD: E. Bratkovskaya et al., hep-ph/0409071 X. Dong, S. Esumi, et al., Phys. Lett. B597, 328(2004).

corrected for e± from decay M. Kaneta et al, J.Phys. G30, S1217(04)

Systematic errors are important!


Conclusions

1) Both direct open charm reconstruction and indirect charm semi-leptonic decay electrons are measured at STAR in d+Au collisions. They provide consistent results.

2) Total charm cross section from this measurement is higher than NLO pQCD calculations.

3) Preliminary D meson spectrum appears to imply a unusual hard fragmentation function for charm quarks.

4) Study open charm v2 and J/ yields to address thermalization issues at RHIC. The run-IV data will just do that.


Upgrade at STAR

STAR MRPC - TOF STAR Heavy Flavor Tracker

1) Full open charm measurements2) Full resonance measurements with both hadron and

lepton decays

open charm measurements from star

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