Haibin Zhang Brookhaven National Laboratory

1. Haibin ZhangBrookhaven National Laboratory Open Charm Production at STAR for The STAR Collaboration 1

2. 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

3. 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

4. ● 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

5. (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

6. D Mesons d+Au minbias collisions @ 200GeV STAR Preliminary 6

7. Time of Flight Hadron identification: STAR Collaboration, nucl-ex/0309012 Electron identification: TOFr |1/ß-1| < 0.03 TPC dE/dx electrons!!! 7

8. 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

9. 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

10. 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

11. 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) 11

12. 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

13. 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 13

14. 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 14