1. Zhangbu Xu, BNLJuly 28 th, ISMD2004 1 Open Charm Production at RHIC Zhangbu Xu BNL Outline  Why Open Charm  Measurements:  Direct/semileptonic  p+p, d+Au, Au+Au  What issues addressed  Conclusions

2. Zhangbu Xu, BNLJuly 28 th, ISMD2004 2 How much do we know? PHENIX, PRL 91, 241803(2003) STAR, PRL 92, 171801(2004) π 0 measurements are consistent with NLO pQCD calculation! Charm should be better!! D mesons,  ’,  Q>3GeV down to low pT pQCD? PDF? FF? Total Cross Section is Insensitive to FF!

3. Zhangbu Xu, BNLJuly 28 th, ISMD2004 3 Initial Charm Production in A+A sensitive to Initial Nuclear Effects Z. Lin & M. Gyulassy, PRL 77 (1996) 1222 dN/dMdy ratio (Sh/no Sh) Charm quark mostly produced from the initial fusion of partons (mostly gluons) Z. Lin & M. Gyulassy, PRC 51 (1995) 2177

4. Zhangbu Xu, BNLJuly 28 th, ISMD2004 4 Heavy Quark as Unique Probe in A+A Collisions M. Djordevic & M. Gyulassy QM04, nucl-th/0404006 V. Greco, C.M. Ko, R. Rapp, nucl-th/0312100 ● Heavy Quark Flow Effects ● Heavy Quark has less dE/dx due to suppression of small angle gluon radiation Y. Dokshitzer &D. Kharzeev PLB519(199)2001

5. Zhangbu Xu, BNLJuly 28 th, ISMD2004 5 “Dead Cone”-- Conclusions The upcoming D meson data for 200 GeV D-Au and Au-Au results will soon become available. According to our results, charm quark suppression should be small ~ 0.6-0.8. Therefore, this suppression should be definitely much smaller than the already observed pion suppression (0.2). If this result is confirmed, then Jet Tomography of QGP will pass another stringent test. On the other hand, if the prediction is falsified, then either the tomographic or the QGP paradigm will have to be revised or abandoned. Magdalena Djordjevic and Miklos Gyulassy, QM04

6. Zhangbu Xu, BNLJuly 28 th, ISMD2004 6 J/ψ production: suppression/enhancement? A. Andronic et. al. PLB 571,36(2003) R.L. Thews et. al. PRC 63, 054905(2003) Charm input from pQCD

7. Zhangbu Xu, BNLJuly 28 th, ISMD2004 7 Why Open Charm?  What creates Heavy Quarks?  Which Nuclear Effect dominates production?  How Heavy Quarks fragment?  Do Heavy Quarks thermalize in QGP?  Whether Heavy Quark and Light Quark Energy Losses are the same?  Total Cross Section  pT spectra  p+p  p+A (d+A)  A+A  Energy/rapidity

8. Zhangbu Xu, BNLJuly 28 th, ISMD2004 8 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 hep-ex/0307080 CHARM is hard to get!

9. Zhangbu Xu, BNLJuly 28 th, ISMD2004 9 D 0 direct reconstruction Event mixing technique ( Br. 3.83%) C. Adler et al., Phys. Rev. C 66, 061901(R)(2002) H. Zhang, J. Phys. G 30, S577(2004) First Direct Open Charm Reconstruction at RHIC STAR Preliminary L. Ruan QM04 H. Zhang DNP03

10. Zhangbu Xu, BNLJuly 28 th, ISMD2004 10 Hadron identification: STAR Collaboration, nucl-ex/0309012 A New Hadron-Blind Detector Electron identification: TOFr |1/ß-1| < 0.03 TPC dE/dx electrons!!! electrons L. Ruan QM04

11. Zhangbu Xu, BNLJuly 28 th, ISMD2004 11 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 π 0 Dalitz decay, background spectra are obtained from data using kinematical selection of the pairs in TPC γ conversion π 0, η Dalitz decays Kaon decays ρ ω Φ vector meson decays heavy quark semi-leptonic decay others Single Electrons Spectra γ conversion and π 0 Dalitz decays are the dominant sources at low pt region. background signal L. Ruan QM04 X. Dong BNL Seminar

12. Zhangbu Xu, BNLJuly 28 th, ISMD2004 12 Background contribution STAR Preliminary An increasing excess found at higher pT region, p T > 1.0 GeV/c,  as expected to be contribution of semileptonic decay from heavy flavor hadrons L. Ruan QM04 X. Dong BNL Seminar

13. Zhangbu Xu, BNLJuly 28 th, ISMD2004 13 Direct/semilepton Spectra Combined fit for D0 and electrons PYTHIA: MSEL = 1, CTEQ5M1  Good agreement between D 0 and electrons spectra!  d+Au and p+p do not show significant nuclear effect STAR Preliminary L. Ruan QM04 X. Dong BNL Seminar

14. Zhangbu Xu, BNLJuly 28 th, ISMD2004 14 Charm production 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 ) L. Ruan QM04 X. Dong BNL Seminar

15. Zhangbu Xu, BNLJuly 28 th, ISMD2004 15 Electron Spectra

16. Zhangbu Xu, BNLJuly 28 th, ISMD2004 16 Open charm spectrum is hard ! Phenix: Phys. Rev. Lett. 88, 192303(2002) D. Kharzeev,hep-ph/0310358 B decay dominated region D 0, D*, D  A. Tai, A. Suaide, QM04

17. Zhangbu Xu, BNLJuly 28 th, ISMD2004 17 Charm quark hadronization at RHIC NLO pQCD predictions: R. Vogt, hep-ph/0203151 bare c-quark spectrum, normalized to measured dn/dy MRST HO Peterson’s function ε=0.06 c quark =4,3,2,1 (GeV)^2 After and fragmentation Higher order pQCD is in need or charm hadronization through fragmentation+recombination (R. Rapp and E. Shuryak hep-ph/0301245) ? A. Tai QM04

18. Zhangbu Xu, BNLJuly 28 th, ISMD2004 18 PHENIX Ability to Study Charm -- electron and muon measurement  high resolution tracking and momentum measurement from Drift chamber. Good electron identification from Ring Imaging Cherenkov detector (RICH) and Electromagnetic Calorimeter (EMCal). Good momentum resolution and muon identification from  ID and  Trk. Open charm. flow of charm. J/  ’ Upsilon High rate capability X. Wei for PHENIX (RHIC/AGS Users’ Meeting)

19. Zhangbu Xu, BNLJuly 28 th, ISMD2004 19 Charm semileptonic decay in PHENIX Subtraction of “photonic” sources. conversion of photons from hadron decays in material Dalitz decays of light mesons (      ) Converter method Comparison of e +/- spectra with and without converter allows separation of photonic and non-photonic sources of single electrons. measurement via  -e coincidences Yield of  -e in vicinity of  mass with mixed event subtraction  -e invariant mass γ e+e+ e-e- Converter Au X. Wei for PHENIX (RHIC/AGS Users’ Meeting)

20. Zhangbu Xu, BNLJuly 28 th, ISMD2004 20 Are Things Consistent?  cc =709  b±85(stat) (sys) +332 -281 PYTHIA ISR NLO pQCD (M. Mangano et al., NPB405(1993)507) PHENIX PRELIMINARY PHENIX data is consistent with the prediction of NLO pQCD calculation and PYTHIA prediction. -- X. Wei for PHENIX (RHIC/AGS Users’ Meeting) Most of the recent calculation indicates  cc  300  b with reasonable parameters

21. Zhangbu Xu, BNLJuly 28 th, ISMD2004 21 Scaling of Electron Spectra Au-Au  s = 200 GeV 1/T AA 1/T AB EdN/dp 3 [mb GeV -2 ] data seems to scale with N coll in all the centrality bins Yellow band represents the set of alpha values consistent with the data at 90% Confidence Level dN/dy = A (N coll )  0.906 <  < 1.042 X. Wei for PHENIX (RHIC/AGS Users’ Meeting)

22. Zhangbu Xu, BNLJuly 28 th, ISMD2004 22 Charm Flow PHENIX PRELIMINARY PHENIX RUN2 data can not distinguish different scenario due to low statistics. From RUN4, both STAR and PHENIX can do better in charm v2 measurements STAR charm scaled up to Au+Au with thermal model for J/  M. Kaneta QM04

23. Zhangbu Xu, BNLJuly 28 th, ISMD2004 23 Conclusions  Open charm yields were measured in d+Au collisions from both direct reconstruction and charm decayed electrons.  These measurements indicate a large total charm production cross-section at RHIC. (STAR>NLO, PHENIX=NLO)  Charm production seems to scale with Nbin collisions  Hard Charm Spectra is observed.  Data from run4 Au+Au will address the medium effects

24. Zhangbu Xu, BNLJuly 28 th, ISMD2004 24 Consistency between electron data sets  STAR systematically (slightly) above PHENIX  beware: error bars are meant to be taken seriously!