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Open charm cross section and R_AA

Open charm cross section and R_AA. Zhangbu Xu (BNL) for the STAR Collaboration. Charm Total Cross Sections Nuclear Effects Conclusions. M c ,b  1.5 GeV>> T c , L QCD , M uds M/E>>0. Hadron identification: STAR Collaboration, nucl-ex/0309012.

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Open charm cross section and R_AA

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  1. Open charm cross section and R_AA Zhangbu Xu (BNL) for the STAR Collaboration • Charm Total Cross Sections • Nuclear Effects • Conclusions Mc,b1.5 GeV>>Tc, LQCD, Muds M/E>>0 PANIC05, Zhangbu Xu (BNL)

  2. Hadron identification: STAR Collaboration, nucl-ex/0309012 Time Projection Chamber: 45 padrow, 2 meters (radius), s(dE/dx)8%, -1<<1 Multi-gap Resistive Plate Chamber TOFr: 1 tray (~1/200), s(t)=85ps PANIC05, Zhangbu Xu (BNL)

  3. electrons hadrons d K p p electrons electrons hadrons Electron ID in STAR – EMC • TPC: dE/dx for p > 1.5 GeV/c • Only primary tracks • (reduces effective radiation length) • Electrons can be discriminated well from hadrons up to 8 GeV/c • Allows to determine the remaining hadron contamination after EMC • EMC: • Tower E ⇒ p/E • Shower Max Detector (SMD) • Hadrons/Electron shower develop different shape • Use # hits cuts • h discrimination power ~ 103-105 Jaro Bielcik QM05

  4. ( Br. 3.83%) D0 direct reconstruction Direct Open Charm Reconstruction at RHIC Event mixing technique C. Adler et al., Phys. Rev. C 66, 061901(R)(2002) J. Adams et al., Phys. Rev. Lett. 94 (2005)062301 PANIC05, Zhangbu Xu (BNL)

  5. d+Au Charm Total Cross Section Data provide reference for Au+Au data STAR >3x PYTHIA,pQCD Energy dependence mR and mF? Need smaller errors to constrain pQCD and determine the effects in Cosmic Ray Showers X. Dong USTC Can we confirm or rule out Cosmic Ray experiments (Pamir, Muon, Tian Shan) under similar conditions? Pamir, Nuovo Cim 24c (2001) 557; NPB 122(2003) 353c PANIC05, Zhangbu Xu (BNL)

  6. D0 Signal in Au+Au Collisions Event-mixing background subtracted invariant mass spectrum fit with gaussian + Linear function A 4.5 D0 signal observed at pT<3 GeV and |y|<1 from 14M Au+Au minbias collision events Three signals also seen in sub-pT ranges with ~2.5 significances Haibin Zhang QM05 6 PANIC05, Zhangbu Xu (BNL)

  7. Dominant source at low pT Mass(e+e-)<0.15 GeV/c2 Electron Spectrum γ conversion π0Dalitz decay η Dalitz decay Kaon decay vector meson decays • Combinatorial background reconstructed by track rotating technique. • Invariant mass < 0.15 for photonic background. Yifei Zhang 8 PANIC05, Zhangbu Xu (BNL)

  8. Charm pT Spectra D0 and e combined fit <pT>=1.10  0.05(stat.) GeV/c in minbias Au+Au <pT>=1.32  0.08(stat.) GeV/c in d+Au Haibin Zhang QM05 9 PANIC05, Zhangbu Xu (BNL)

  9. Charm Total Cross Section Charm total cross section per NN interaction STAR Preliminary 1.11 0.08(stat.)  0.42(sys.) mb in 200GeV minbias Au+Au collsions 1.4  0.2(stat.)  0.4(sys.) mb in 200GeV minbias d+Au collisions Charm total cross section follows roughly Nbin scaling from d+Au to Au+Au considering errors Indication of charm production in initial collisions Haibin Zhang, Xin Dong QM05 NLO pQCD from R. Vogt 10 PANIC05, Zhangbu Xu (BNL)

  10. RAA of non-photonic electrons STAR Highlight talk • Evidence of large heavy quark energy loss! PANIC05, Zhangbu Xu (BNL)

  11. M. Djordjevic, et. al. nucl-th/0507019 N. Armesto et. al. private comm. any beauty? Challenges to theory Current energy loss mechanisms can only account for part of strong suppression of RAA for electrons. PANIC05, Zhangbu Xu (BNL)

  12. STAR Preliminary STAR Preliminary Photonic background Photonic background matches with inclusive electrons. → Consistent with low charm yield at 62.4 GeV PANIC05, Zhangbu Xu (BNL)

  13. Muon ID at low pT p e m 0.15<pT<0.25 GeV/c, DCA<3cm PANIC05, Zhangbu Xu (BNL)

  14. Conclusions • Charm cross sections measured in p+p, d+Au and Au+Au: binary scaling=> charm production at initial impact • Large suppression of HF->e spectra in Au+Au • Heavy Flavor measurements at RHIC, new challenges to theory. • Continue developments of new measurements and upgrades! PANIC05, Zhangbu Xu (BNL)

  15. Effects related to Open Charm Down Down Up Up Down Up Up Down Down Up? • Radiation Energy Loss • Collision Energy Loss • Dead Cone Effect • Ter-Mikayelian Effect • Transition Radiation • Flow (radial & elliptic) • (quark) Coalescence • Death of “dead cone” • Charm Resonance • CGC All these happen at intermediate pTEmphasize on experimental measurements PANIC05, Zhangbu Xu (BNL)

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