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Jaroslav Biel čí k for STAR collaboration Czech Technical University & NPI ASCR Prague

The study of heavy flavors via non-photonic electrons in STAR. Jaroslav Biel čí k for STAR collaboration Czech Technical University & NPI ASCR Prague. 34-th International Conference on High Energy Physics 2008 Philadelphia, PA, USA. Outline.

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Jaroslav Biel čí k for STAR collaboration Czech Technical University & NPI ASCR Prague

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  1. The study of heavy flavors via non-photonic electrons in STAR Jaroslav Bielčík for STAR collaboration Czech TechnicalUniversity & NPI ASCR Prague 34-th International Conference on High Energy Physics 2008 Philadelphia, PA, USA

  2. Outline • Motivation for heavy flavor physics • Spectra • Charm mesons: D0 • Non-photonic electrons • Energy loss • Summary jaroslav.bielcik@fjfi.cvut.cz

  3. partons interact with medium • gluon radiation/energyloss • measuring high-pT particles in Au+Au vs. p+p • to extract the properties of medium Probing of dense nuclear matter with jets Au+Au Collision p+p Collision • nuclear modification factor RAA : Average number of NN collisions in AA collision • No “Effect” of nuclear matter: • RAA = 1 at higher momenta where • hard processes dominate • Suppression: RAA < 1 jaroslav.bielcik@fjfi.cvut.cz

  4. Hadron suppression in central Au+Au • Direct photons: • not suppressed, do not interact • binary scaling works • Hadron yields: • strongly suppressed • in central Au+Au at 200 GeV • Large energy loss of light partons • in the formed nuclear matter Energy loss depends on properties of medium (gluon densities, size) properties of “probe” (color charge, mass) jaroslav.bielcik@fjfi.cvut.cz

  5. parton light ENERGY LOSS hot and dense medium M.Djordjevic PRL 94 (2004) Heavy quarks as a probe • p+p data:  baseline of heavy ion measurements  test of pQCD calculations • Due to their large mass heavy quarks are primarily produced by gluon fusion in early stage of collision  production rates calculable by pQCDM. Gyulassy and Z. Lin, PRC 51, 2177 (1995) • heavy ion data: • Studying energy loss of heavy quarks  independent way to extractproperties of the medium dead-cone effect: jaroslav.bielcik@fjfi.cvut.cz Dokshitzer and Kharzeev, PLB 519, 199 (2001)

  6. Open heavy flavor Direct: reconstruction of all decay products Indirect: charm and beauty via electrons • c  e+ + anything(B.R.: 9.6%) • b  e+ + anything(B.R.: 10.9%) • issue of photonic background charm (and beauty) via muons • c  + + anything (B.R.: 9.5%) jaroslav.bielcik@fjfi.cvut.cz

  7. STAR detector Most relevant for presented results: • TPC(tracking,p,dEdx) • || < 1.5 • p/p = 2-4% • dE/dx/dEdx = 8% • BEMC (energy, trigger) • || < 1 • dE/E ~ 16%/E • Shower maximum detector jaroslav.bielcik@fjfi.cvut.cz

  8. D0 Phys. Rev. Lett. 94 (2005) Direct D-meson reconstruction at STAR STAR arXiv:0805.0364 • K invariant mass distribution in d+Au, Au+Au, Cu+Cu at 200 GeV collisions • No topological analysis => only pT<3.3 GeV/c jaroslav.bielcik@fjfi.cvut.cz

  9. Measurement of charm cross section AuAu 200 GeV STAR arXiv: 0805.0364 • STAR charm cross section: combined fit of muons, D0 and low pT electrons •  90% of total kinematic range covered • Low pT muons constrain charm cross-section jaroslav.bielcik@fjfi.cvut.cz

  10. STAR High pT non-photonic electrons • High-tower EMC trigger • => high pT electrons • FONLL scaled by ~5, • describes shape of p+p spectra well • suggesting bottomcontribution STARPhys. Rev. Lett. 98 (2007) 192301 Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys. Rev. Lett. 97 (2006) 252002 jaroslav.bielcik@fjfi.cvut.cz

  11. Charm cross-section at 200 GeV STAR data in various systems  observation of binary scaling Consistent with NLO calculation  however uncertainties are huge STAR x PHENIX results ~ factor 2 difference jaroslav.bielcik@fjfi.cvut.cz

  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 Non-photonicelectrons suppression Nuclear modification factor Non-photonic electrons suppression similar to hadrons pT (NPE) < pT (D NPE) jaroslav.bielcik@fjfi.cvut.cz

  13. Non-photonic electrons in Cu+Cu 200GeV preliminary preliminary Cu+Cu 200 GeV: • <Nbinary >~ 82 for 0-54% • RAA ~ 0.6 - 0.7 for pT > 3 GeV/c jaroslav.bielcik@fjfi.cvut.cz

  14. Consistency with Au+Au 200GeV results • Consistent with Au+Au 200 GeV data for similar Npart • Consistent with p ±RAA in Cu+Cu 200 GeV RAA for non-photonic e± RAA for p ±, Cu+Cu 200 GeV Non-photonic e± Cu+Cu 200 GeV 0-54% * STAR preliminary jaroslav.bielcik@fjfi.cvut.cz STAR: PRL 98 (2007) 192301 PHENIX: PRL 98 (2007) 172301

  15. STARPhys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301 Radiative energy loss • 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) jaroslav.bielcik@fjfi.cvut.cz

  16. 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) jaroslav.bielcik@fjfi.cvut.cz

  17. 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? jaroslav.bielcik@fjfi.cvut.cz

  18. Relative bottom contribution (be)/(ce+be) • Difficult to interpret suppression without the knowledge of bottom vs. charm relative ratio • Data shows non-zero bottom contribution • Good agreement among different analyses. • Relative b/(b+c) ratio consistent with FONLL. jaroslav.bielcik@fjfi.cvut.cz

  19. Conclusions • Heavy flavor is an important tool to understand HI physics at RHIC • STAR results are interesting and challenging charm cross section • Binary scaling in charm production produced in initial phase • FONLL is consistent with data • STAR/PHENIX discrepancy RUN 8 data on tape non-photonic electrons • Strong high-pTsuppression in Au+Aularge energy loss of c • b contribution consistent with FONLL important b contribution • Cu+Cu and Au+Au results consistent • heavy quark energy loss not understood • How much is b suppressed? Not clear yet. also large uncertainties jaroslav.bielcik@fjfi.cvut.cz

  20. Bottom suppression from data No experimental evidence that bottom is suppressed more than predicted jaroslav.bielcik@fjfi.cvut.cz T.Ullrich Hard Probes 2008

  21. BRAHMS PHOBOS PHENIX STAR Relativistic Heavy Ion Collider RHIC site in BNL on Long Island RHIC has been exploring nuclear matter at extreme conditions over the last few years Lattice QCD predicts a phase transition from hadronic matter to a deconfined state, the Quark-Gluon Plasma Colliding systems: p+p, d+Au, Cu+Cu, Au+Au Energies √sNN = 20, 62, 130, 200GeV STAR jaroslav.bielcik@fjfi.cvut.cz

  22. PRL 98, 172301 (2007) Estimating h/s • transport models • Rapp & van Hees (PRC 71, 034907 (2005)) • diffusion coefficient required for simultaneous fit of RAA and v2 • DHQx2pT ~ 4-6 • Moore & Teaney (PRC 71, 064904 (2005)) • difficulties to describe RAA and v2 simultaneously • calculate perturbatively (and argue that plausible also non-perturbatively) • DHQ/ (h/(e+P)) ~ 6 (for Nf = 3) • at mB = 0 • e + P = Ts • then • h/s = (1.3-2.0)/4p jaroslav.bielcik@fjfi.cvut.cz

  23. R. Lacey et al.: PRL 98:092301, 2007 S. Gavin and M. Abdel-Aziz: PRL 97:162302, 2006 H.-J. Drescher et al.: arXiv:0704.3553 pTfluctuations STAR v2 PHOBOS v2 PHENIX & STAR conjectured quantum limit Comparison with other estimates • estimates of h/s based on flow and fluctuation data • indicate small value as well • close to conjectured limit • significantly below h/s of helium (4ph/s ~ 9) jaroslav.bielcik@fjfi.cvut.cz

  24. Charm ~ y jaroslav.bielcik@fjfi.cvut.cz

  25. 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 jaroslav.bielcik@fjfi.cvut.cz

  26. 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 jaroslav.bielcik@fjfi.cvut.cz

  27. Extraction of the cross-section Number of binary collisions (Glauber) Inelastic cross-section in p+p (UA5) Conversion to full rapidity (Pythia) Ratio obtained from e+e- collisions STAR Preliminary:

  28. 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 jaroslav.bielcik@fjfi.cvut.cz

  29. 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 jaroslav.bielcik@fjfi.cvut.cz

  30. sCC: comparison with other measurements jaroslav.bielcik@fjfi.cvut.cz

  31. jaroslav.bielcik@fjfi.cvut.cz

  32. Combined Fit D0, e , combined fit Power-law function with parameters dN/dy, <pT> and n to describe the D0 spectrum Generate D0e decay kinematics according to the above parameters Vary (dN/dy, <pT>, n) to get the min. 2 by comparing power-law to D0 data and the decayed e shape to e and  data Spectra difference between e and  ~5% (included into sys. error) Advantage: D0 and  constrain low pT e constrains higher pT jaroslav.bielcik@fjfi.cvut.cz

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