Haibin Zhang Hot Quarks 2004, July 22nd, 2004

STAR

Haibin ZhangBrookhaven National Laboratory

Open Charm Production at STAROpen Charm Production at STAR

1

for

The STAR Collaboration

Haibin Zhang Hot Quarks 2004, July 22nd, 2004

STAROutline

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Motivations

D0, D*±, D± open charm measurement in d+Au collisions

Single electron spectra in p+p and d+Au collisions

Charm cross sections

Open charm pT spectrum and theoretical comparisons

Summary

Haibin Zhang Hot Quarks 2004, July 22nd, 2004

STAR

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Motivation (I)

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

Through leptonic decay channel of open charm, sensitive to shadowing

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

dN

/dM

dy

rati

o (S

h/n

o S

h)

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

Haibin Zhang Hot Quarks 2004, July 22nd, 2004

STAR

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Motivation (II)

“enhancement of D0/ in HOT matter”

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

● Charm quark found to loose only ~10% of their energy during propagation at RHIC energy

Y.L. Dokshizer & D.E. KharzeevPLB 519 (2001) 199

Haibin Zhang Hot Quarks 2004, July 22nd, 2004

STAR

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Time Projection Chamber

TPC

TOFr

Event mixing techniqueC. Adler et al., Phys. Rev. C 66, 061901(R)(2002)H. Zhang, J. Phys. G 30, S577(2004)

%)1.9(KD

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

%)8.3(0 KD

(6.2%)

Haibin Zhang Hot Quarks 2004, July 22nd, 2004

STARD Mesons

d+Au minbias collisions @ 200GeV

STAR Preliminary

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Haibin Zhang Hot Quarks 2004, July 22nd, 2004

STAR

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Time of Flight

Hadron identification: STAR Collaboration, nucl-ex/0309012

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

Haibin Zhang Hot Quarks 2004, July 22nd, 2004

STAR

TPCFor 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

Electron Background

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Haibin Zhang Hot Quarks 2004, July 22nd, 2004

STAR

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Electrons

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

STAR Preliminary

Haibin Zhang Hot Quarks 2004, July 22nd, 2004

STARSpectra

Combining fit forD0 and electrons

PYTHIA: MSEL = 1, CTEQ5M1

Good agreement between D0 and electrons spectra!d+Au and p+p do not show significant nuclear effect

STAR Preliminary

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Haibin Zhang Hot Quarks 2004, July 22nd, 2004

STARCharm Cross Section

NLO pQCD calculation under-predict the ccbarproduction cross sectionat RHIC

Power law for ccbar productionCross section from SPS->RHIC n = 1.9 +- 0.2

( 0.3 for charged multiplicity)

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Haibin Zhang Hot Quarks 2004, July 22nd, 2004

STARCharm pT Spectrum

Open symbol D+/D0

Solid symbol D*/D0

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Charm pT spectrum can be fit well by the power-law function

Charm meson ratios consistent with models and previous measurements

Haibin Zhang Hot Quarks 2004, July 22nd, 2004

STARCharm pT Spectrum

NLO order calculation was done by R. Vogt and FONLL code

(fixed order NLO and resummations of next-to-leading logs)

was obtained from M. Cacciaria and P. Nason, hep-ph0306212

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Scaled to STAR measured cross section

The measured D pt spectrum shape

coincides with the bare-quark distribution

from the NLO calculation.

Data favor a fragmentation function

peaked at x~ 1

Haibin Zhang Hot Quarks 2004, July 22nd, 2004

STAR

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Summary

Direct open Charm D0, D* and D± were measured in d+Au collisions

Single electron measurements agree with STAR direct D measurements well.

These measurements indicate a large total charm production cross-section at RHIC. NLO pQCD calculations underpredict this value.

The D pT spectrum shape coincides with the bare-quark dis- tribution from the NLO calculation