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Open Charm Production at RHIC

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. PHENIX, PRL 91, 241803(2003). STAR, PRL 92, 171801(2004). D mesons. , Y ’, c. Q>3GeV down to low pT.

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Open Charm Production at RHIC

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  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. PHENIX, PRL 91, 241803(2003) STAR, PRL 92, 171801(2004) D mesons , Y’, c Q>3GeV down to low pT How much do we know? PDF? pQCD? FF? Total Cross Section is Insensitive to FF! π0 measurements are consistent with NLO pQCD calculation! Charm should be better!!

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

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

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

  7. 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 Why Open Charm?

  8. Low-energy fixed target – direct D measurement CDF directy D measurement -- high pT Fermilab E769, PRL 77, 2388 (1996) hep-ex/0307080 Previous Experiments CHARM is hard to get! 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

  9. ( Br. 3.83%) D0 direct reconstruction STAR Preliminary First Direct Open Charm Reconstruction at RHIC Event mixing technique C. Adler et al., Phys. Rev. C 66, 061901(R)(2002) H. Zhang, J. Phys. G 30, S577(2004) L. Ruan QM04 H. Zhang DNP03

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

  11. 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 Measurements of electron background • Background Topology: • TOFr tagged e+/e- • Large TPC acceptance • High efficiency of reconstructing • electron pair For the γconversion and π0 Dalitz decay, background spectra are obtained from data using kinematical selection of the pairs in TPC L. Ruan QM04 X. Dong BNL Seminar

  12. Background contribution STAR Preliminary An increasing excess found at higher pT region, pT > 1.0 GeV/c, asexpected to be contribution of semileptonic decay from heavy flavor hadrons L. Ruan QM04 X. Dong BNL Seminar

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

  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. Electron Spectra

  16. B decay dominated region Open charm spectrum is hard ! D0, D*, D A. Tai, A. Suaide, QM04 STAR preliminary Phenix: Phys. Rev. Lett. 88, 192303(2002) D. Kharzeev,hep-ph/0310358

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

  18. PHENIX Ability to Study Charm -- electron and muon measurement X. Wei for PHENIX (RHIC/AGS Users’ Meeting) • 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 mID and mTrk. High rate capability • Open charm. • flow of charm. • J/y, y’ • Upsilon

  19. e+ γ e- Converter -einvariant mass Au Au Charm semileptonic decay in PHENIX • Subtraction of“photonic” sources. • conversion of photons from hadron decays in material • Dalitz decays of light mesons (p0, h, w, h, f) • 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 X. Wei for PHENIX (RHIC/AGS Users’ Meeting)

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

  21. 1/TABEdN/dp3 [mb GeV-2] 1/TABEdN/dp3 [mb GeV-2] 0.906 <  < 1.042 1/TAA 1/TAA Yellow band represents the set of alpha values consistent with the data at 90% Confidence Level dN/dy = A (Ncoll) 1/TABEdN/dp3 [mb GeV-2] 1/TABEdN/dp3 [mb GeV-2] 1/TABEdN/dp3 [mb GeV-2] 1/TABEdN/dp3 [mb GeV-2] 1/TAA 1/TAA 1/TAA Scaling of Electron Spectra Au-Au s = 200 GeV X. Wei for PHENIX (RHIC/AGS Users’ Meeting) • data seems to scale with Ncoll in all the centrality bins

  22. PHENIX PRELIMINARY STAR charm scaled up to Au+Au with thermal model for J/ Charm Flow 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 M. Kaneta QM04

  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) • Hard Charm Spectra is observed. • Charm production seems to scale with Nbin collisions • Data from run4 Au+Au will address the medium effects

  24. Consistency between electron data sets • STAR systematically (slightly) above PHENIX • beware: error bars are meant to be takenseriously!

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