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Exploring Open Heavy Flavor with STAR Detector at RHIC & AGS User’s Meeting 2007

This presentation delves into the study of open heavy flavor using the STAR detector at the RHIC & AGS User’s Meeting 2007, focusing on aspects like energy loss, charm and beauty quarkonia reconstruction, and muon measurements in hot and dense mediums. It discusses the unique properties of heavy quarks in production rates, energy loss mechanisms, and cross-section measurements, highlighting their significance in understanding the behavior of heavy quarks in the medium. Key topics include direct and indirect heavy flavor reconstruction, D/Ds peak analyses, non-photonic electrons, and the role of collisional energy loss in the context of heavy quark interactions. The presentation provides insights into the current understanding of heavy quark properties and their behavior in high-energy collisions.

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Exploring Open Heavy Flavor with STAR Detector at RHIC & AGS User’s Meeting 2007

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  1. Open heavy flavor with the STAR detector Jaroslav Bielcik Yale for STAR collaboration Heavy Flavor and Quarkonia Production Workshop RHIC&AGS User’s meeting 2007

  2. parton light ENERGY LOSS hot and dense medium M.Djordjevic PRL 94 (2004) Heavy quarks as a probe • Studying energy loss of heavy quarks  independent way to extractproperties of the medium • Due to their large mass heavy quarks are primarily produced by gluon fusion production rates calculable by pQCD sensitive to initial gluon distribution M. Gyulassy and Z. Lin, PRC 51, 2177 (1995) • Heavy quarks lose less energy due to suppression of small angle gluon radiation (dead-cone effect)Dokshitzer and Kharzeev, PLB 519, 199 (2001) • Amount of collisional and radiative energy losses seems to be similarM.G. Mustafa, PRC72, 014905 2007 RHIC&AGS Annual Users' Meeting

  3. Open heavy flavor Direct: reconstruction of all decay products Indirect: charm and beauty electrons • c  e+ + anything(B.R.: 9.6%) • b  e+ + anything(B.R.: 10.9%) charm (and beauty) muons • c  + + anything (B.R.: 9.5%) AzimuthalCorrelations: e-h, e-D 2007 RHIC&AGS Annual Users' Meeting

  4. D0 STAR Phys. Rev. Lett. 94 (2005) Charm via hadronic decays d+Au Au+Au TPC only • D0 in d+Au and Au+Au at 200GeV (pT 0.1- 3.0 GeV/c) 2007 RHIC&AGS Annual Users' Meeting

  5. STAR Preliminary D0 + D0 in Cu+Cu at 200GeV TPC only Significance 2007 RHIC&AGS Annual Users' Meeting

  6. D/Ds Peak in d+Au TPC only STAR Preliminary Ds+ D+ Ds+ Significance D+ Significance • No negatively charged D or Ds found yet 2007 RHIC&AGS Annual Users' Meeting

  7. Muon measurement 0.17 < pT < 0.21 GeV/c 0-12% Au+Au   minv2 (GeV2/c4) Inclusive   from charm  from  / K (simu.) Signal+bg. fit to data • Low-pT (pT < 0.25 GeV/c) muons can be measured with TPC + ToF • - this helps to constrain charm cross-section • Separate different muon contributions using MC simulations: • K and  decay • charm decay • DCA (distance of closest approach) distribution is very different TPC+TOF m2=(p/b/g)2 (STAR), Hard Probes 2006 2007 RHIC&AGS Annual Users' Meeting

  8. Non-photonic electrons (part I) Au+Au TPC+TOF • Photonic background must • be reconstructed and subtracted • only TOF patch Df=p/30 • instrumented • non-photonic electrons: • pT 0.9-5.0 GeV/c • D0+electrons+muons • 90% of total kinematic range covered 2007 RHIC&AGS Annual Users' Meeting

  9. STAR Preliminary • 0.94  0.18(stat.) mb • in 200GeV minbias Cu+Cu The cross sections follow binary scaling, signature of  charm production exclusively at the initial impact. Charm total cross sections • 1.4  0.2(stat.)  0.4(sys.) mb in 200GeV minbias d+Au • 1.29  0.12  0.36 mb in 200GeV minbias Au+Au • 1.40  0.11  0.39 mb in 200GeV central 12% Au+Au • FONLL underestimates measured • cross-section by factor ~5 2007 RHIC&AGS Annual Users' Meeting

  10. STAR Non-photonic electrons (part II) • High-tower EMC trigger • => high pT electrons • Photonic electrons reconstructed • and subtracted • FONLL scaled by ~5,, • describes shape of p+p spectra well • suggesting bottomcontribution TPC+EMC Phys. Rev. Lett. 98 (2007) 192301 2007 RHIC&AGS Annual Users' Meeting

  11. Non-photonic electrons vs. FONLL • FONLLunderestimates measured • electrons by factor 4-5 • PHENIX high-pT data differs from • STAR by factor 2 Non-photonic electrons p+p 200 GeV • not understood yet • STAR low material run planned STARPhys. Rev. Lett. 98 (2007) 192301 PHENIX Phys. Rev. Lett. 97 (2006) 252002 2007 RHIC&AGS Annual Users' Meeting

  12. STARPhys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301 STAR hadrons pT> 6 GeV/c d+Au: no suppression expected  slight enhancement expected (Cronin effect) Peripheral Au+Au: no suppression expected Central Au+Au: little suppression expected ?! Semi-Central Au+Au: very little suppression expected RAA from d+Au to central Au+Au Nuclear modification factor 2007 RHIC&AGS Annual Users' Meeting

  13. STARPhys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301 Electron RAA Radiative energy loss (c+b) • parameters of medium in • models extracted from hadron data • Radiative energyloss alone • in medium with reasonable • parametersdoes not describe • the data • What are the other sources • of energy loss ? • Djordjevic, Phys. Lett. B632 81 (2006) • Armesto, Phys. Lett. B637 362 (2006) 2007 RHIC&AGS Annual Users' Meeting

  14. STARPhys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301 Role of collisional energy loss • Collisional/elastic energy loss may • be importantfor heavy quarks • Still not good agreement at high-pT • Wicks, nucl-th/0512076 • van Hess, Phys. Rev. C73 034913 (2006) 2007 RHIC&AGS Annual Users' Meeting

  15. STARPhys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301 Charm alone? • Since the suppression of • b quark electrons is smaller • charm alone agrees better • What is b contribution? 2007 RHIC&AGS Annual Users' Meeting

  16. STARPhys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301 In medium fragmentation • Other effects may contribute to the • observed suppression • both b+c taken into account • heavy quarks can fragment • inside the medium and can • be suppressed by dissociation • Adil and Vitev, Phys.Lett.B649 (2007) 139 2007 RHIC&AGS Annual Users' Meeting

  17. e-h from B e-h from D Fit Can we tell how much beauty? TPC+EMC • Use e-h Correlation • Large B mass compared to D • Semileptonic decay: e gets larger kick from B • Broadened e-hcorrelation on near-side. • Extract B contribution • Use PYTHIA shapes • Con: Model dependent • Pro: Depends on decay kinematics well described • Fit ratio B/(B+D) p+p 200 GeV nucl-ex/0701050 STAR QM2006 2007 RHIC&AGS Annual Users' Meeting

  18. Relative bottom contribution to nonphotonic electrons vs. pT Bottom ! • Fit e-hcorrelation with PYTHIA D and B • Data shows non-zero B contribution • Contribution consistent with FONLL • Model dependent (PYTHIA) • Depends mainly on kinematics of D/B decay (not on Fragmentation) • Dominant systematic uncertainty: • photonic background rejection efficiency • Additional uncertainties under study p+p 200 GeV STAR QM2006 2007 RHIC&AGS Annual Users' Meeting

  19. Heavy flavor tagged correlations TPC+EMC trigger side • Advantage: STAR has large acceptance (|| < 1 and full azimuth) • Underlying production mechanismcan be identified using second charm/bottom particle • Experimental approach • - non-photonic electrons from semi-leptonic c/b decays are used to trigger on c-cbar or b-bbar pairs • associate D0 mesons are reconstructed via their hadronic decay channel (probe) heavy quark production probe side 2007 RHIC&AGS Annual Users' Meeting

  20. electron-D0 azimuthal correlations p+psNN = 200 GeV, Ldt = 9 pb-1 • Clear D0 signal • - S/B ratio factor ~100 better than signal w/o electron trigger • Near- and away-side correlation peak with similar yields observed •  Evidence for heavy flavor correlations • Next: Separate charm and bottom contribution as well as sub-processes (e.g. gluon splitting) using • - dedicated simulations • - charge-sign requirement on (e, D0) pairs PDG mass D0+D0 STAR nucl-exp 0705.2089 pTele>1.5 GeV/c statistical errors only 2007 RHIC&AGS Annual Users' Meeting

  21. Mid-Term Upgrades at RHIC • Detector Upgrades relevant for heavy flavor physics Machine Upgrade (RHIC-II):Increased luminosity (x 40) via electron cooling See Z.Xu talk on STAR upgrades 2007 RHIC&AGS Annual Users' Meeting

  22. HFT Direct Charm Measurements Spectra vs pT at 10% error Elliptic flow v2 vs pT at 10% error Current data rate: 100x106 per run DAQ1000: x10 rate 2007 RHIC&AGS Annual Users' Meeting

  23. Open bottom B-> J/psi+X • possible with displaced vertex measurement and RHIC II luminosity • enough for measurement of cross section and RAA ~ pT,y • not enough for v2 measurement 12 weeks run; HFT in; D assumes 100Hz min.bias rate 2007 RHIC&AGS Annual Users' Meeting

  24. Conclusions and considerations • Heavy flavor is an important tool to understand HI physics at RHIC • First RHIC results are interesting and challenging • Large differences in cross section between Phenix and STAR • Binary scaling in charm production • Why so much suppression at high-pT? • Charm and bottom relative production. Where bottom starts dominating? • First attempts from STAR indicates a non-zero contribution of bottom to the non-photonic electron spectra • First observation of heavy flavor correlations • Very first step on the understanding of heavy quark energy loss • RHIC II higher-luminosities and detector upgrades • more precise measurements of charm • direct access to bottom physics 2007 RHIC&AGS Annual Users' Meeting

  25. Conversion from dN/dy to Cross-Section p+p inelastic cross section number of binary collisions conversion to full rapidity ratio from e+e- collider data *Systematic error measurement for dN/dy in progress. 2007 RHIC&AGS Annual Users' Meeting

  26. Muon measurement TPC+TOF • There are no photonic muons !!! • pT 0.16-0.26 GeV/c • it is good that it is so low pT 2007 RHIC&AGS Annual Users' Meeting

  27. d+Au: no suppression expected  slight enhancement expected (Cronin effect) Central Au+Au: little suppression expected ?! Peripheral Au+Au: no suppression expected Semi-Central Au+Au: very little suppression expected RAA from d+Au to central Au+Au Phys. Rev. Lett. 98 (2007) 192301 Nuclear modification factor 2007 RHIC&AGS Annual Users' Meeting

  28. STARPhys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301 Electron RAA Radiative energy loss (c+b) • parameters of medium in • models extracted from hadron data • Radiative energyloss alone • in medium with reasonable • parametersdoes not describe • the data • What are the other sources • of energy loss ? • Djordjevic, Phys. Lett. B632 81 (2006) • Armesto, Phys. Lett. B637 362 (2006) 2007 RHIC&AGS Annual Users' Meeting

  29. STARPhys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301 Role of collisional energy loss • Collisional/elastic energy loss may • be importantfor heavy quarks • Still not good agreement at high-pT • Wicks, nucl-th/0512076 • van Hess, Phys. Rev. C73 034913 (2006) 2007 RHIC&AGS Annual Users' Meeting

  30. STARPhys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301 Charm alone? • Since the suppression of • b quark electrons is smaller • charm alone agrees better • What is b contribution? 2007 RHIC&AGS Annual Users' Meeting

  31. STARPhys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301 In medium fragmentation • Other effects may contribute to the • observed suppression • both b+c taken into account • heavy quarks can fragment • inside the medium and can • be suppressed by dissociation • Adil and Vitev, Phys.Lett.B649 (2007) 139 2007 RHIC&AGS Annual Users' Meeting

  32. Uncertainty of c/b relative contribution • FONLL: • Large uncertainty on c/b crossing • 3 to 9 GeV/c Beauty predicted to be significant above 4-5 GeV/c 2007 RHIC&AGS Annual Users' Meeting

  33. 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~1 for e- • Shower Max Detector • Hadrons/Electron shower develop different shape • 85-90% purity of electrons • (pT dependent) all p>1.5 GeV/c2 p/E SMD 2007 RHIC&AGS Annual Users' Meeting

  34. Inclusive/Photonic: • Excess over photonic electrons observed for all system and centralities => non-photonic signal Photonic electrons background • Background:Mainly from g conv and p0,h Dalitz • Rejection strategy: For every electron candidate • Combinations with all TPC electron candidates • Me+e-<0.14 GeV/c2 flagged photonic • Correct for primary electrons misidentified as background • Correct for background rejectionefficiency ~50-60% for central Au+Au 2007 RHIC&AGS Annual Users' Meeting

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