Haibin Zhang Hot Quarks 2004, July 22nd, 2004
STAR
Haibin ZhangBrookhaven National Laboratory
Open Charm Production at STAROpen Charm Production at STAR
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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
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