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Haibin Zhang Brookhaven National Laboratory. Open Charm Production at STAR. for. The STAR Collaboration. 1. Outline. Motivations. D 0 , D* ± , D ± open charm measurement in d+Au collisions. Single electron spectra in p+p and d+Au collisions. Charm cross sections.

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Haibin Zhang Brookhaven National Laboratory

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Haibin zhang brookhaven national laboratory

Haibin ZhangBrookhaven National Laboratory

Open Charm Production at STAR

for

The STAR Collaboration

1


Haibin zhang brookhaven national laboratory

Outline

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

2


Haibin zhang brookhaven national laboratory

Motivation (I)

Through leptonic decay channel of open charm,

sensitive to shadowing

Charm quark mostly produced

from the initial fusion of partons

(mostly gluons)

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

dN/dMdy ratio (Sh/no Sh)

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

3


Haibin zhang brookhaven national laboratory

● 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

Motivation (II)

Y.L. Dokshizer & D.E. Kharzeev

PLB 519 (2001) 199

“enhancement of D0/ in

HOT matter”

4


Haibin zhang brookhaven national laboratory

(6.2%)

Time Projection Chamber

TPC

TOFr

Event mixing technique

C. Adler et al., Phys. Rev. C 66, 061901(R)(2002)

H. Zhang, J. Phys. G 30, S577(2004)

5


Haibin zhang brookhaven national laboratory

D Mesons

d+Au minbias collisions @ 200GeV

STAR Preliminary

6


Haibin zhang brookhaven national laboratory

Time of Flight

Hadron identification:

STAR Collaboration, nucl-ex/0309012

Electron identification:

TOFr |1/ß-1| < 0.03

TPC dE/dx electrons!!!

7


Haibin zhang brookhaven national laboratory

γ conversion

π0, η Dalitz decays

Kaon decays

ρωΦ vector meson decays

heavy quark semi-leptonic decay

others

Single

Electrons

Spectra

background

signal

γ conversion and π0Dalitz decays are the dominant sources at low pt region.

TPC

Electron Background

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

8


Haibin zhang brookhaven national laboratory

Electrons

STAR Preliminary

An increasing excess found at higher pT region, pT > 1.0 GeV/c,

asexpected to be contribution of semi-leptonic decay from heavy flavor hadrons

9


Haibin zhang brookhaven national laboratory

Combining fit for

D0 and electrons

PYTHIA: MSEL = 1, CTEQ5M1

Spectra

STAR Preliminary

  • Good agreement between D0 and electrons spectra!

  • d+Au and p+p do not show significant nuclear effect

10


Haibin zhang brookhaven national laboratory

Charm Cross Section

NLO pQCD calculation

under-predict the ccbar

production cross section

at RHIC

Power law for ccbar production

Cross section from SPS->RHIC

n = 1.9 +- 0.2

( 0.3 for charged multiplicity)

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Haibin zhang brookhaven national laboratory

Open symbol D+/D0

Solid symbol D*/D0

Charm pT Spectrum

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

Charm meson ratios consistent with models and previous measurements

12


Haibin zhang brookhaven national laboratory

Charm pT Spectrum

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

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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Haibin zhang brookhaven national laboratory

  • 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

Summary

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