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Jaroslav Biel čí k Czech Technical University Prague

Open heavy flavor at RHIC. Jaroslav Biel čí k Czech Technical University Prague. High-p T physics at LHC , March 2008 , Tokaj. Outline. Motivation for heavy flavor physics Spectra: Charm mesons: D 0 Non-photonic electrons Heavy flavor e + e - pairs Flow/Energy loss

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Jaroslav Biel čí k Czech Technical University Prague

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  1. Open heavy flavor at RHIC Jaroslav Bielčík Czech Technical University Prague High-pT physics at LHC , March 2008, Tokaj

  2. Outline • Motivation for heavy flavor physics • Spectra: • Charm mesons: D0 • Non-photonic electrons • Heavy flavor e+e-pairs • Flow/Energy loss • Summary QM 2008: Y.Zhang (overview), A. Shabetai (STAR), D. Hornback(PHENIX) R. Averbeck (PHENIX),  Y. Morino (PHENIX) jaroslav.bielcik@fjfi.cvut.cz

  3. 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 flow of heavy quarks  understanding of thermalization • 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)

  4. 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

  5. Charm measurements at RHIC STAR measurements: • Signal/Spectra D0 K • c   + X (y=0, low pT) • c,b  e + X • Flow & energy loss RAA from NPE PHENIX measurements: • Signal/Spectra D0 K-+0 • c   + X (<y>=1.65, pT>1 GeV/c) • c,b  e + X • e+e- • Flow & energy loss Elliptic flow from NPE RAA from NPE jaroslav.bielcik@fjfi.cvut.cz

  6. SPECTRA jaroslav.bielcik@fjfi.cvut.cz

  7. D0 Phys. Rev. Lett. 94 (2005) Direct D-meson reconstruction at STAR STAR Preliminary • K invariant mass distribution in d+Au, Au+Au minbias, Cu+Cu minbias at 200 GeV collisions • No displaced vertex used => only pT<3.3 GeV/c jaroslav.bielcik@fjfi.cvut.cz

  8. PHENIX Preliminary Year5 pp 200 GeV Direct D-meson reconstruction at PHENIX • p+p 200 GeV/c: •  D0K+p-p0 decay channel • p0 identified via p0 gg decay •  Only visible signal in 5<pT<15 GeV/c •  No visible signal below 5 GeV/c and above 15 GeV/c peak is not at right position jaroslav.bielcik@fjfi.cvut.cz

  9. Leptons from HF decay at STAR STAR Preliminary • STAR charm cross section: combined fit of muons, D0 and low pT electrons •  90% of total kinematic range covered • New Cu+Cu D0 spectrum agree with Au+Au after number of binary scaled • Low pT muon constrains charm cross-section jaroslav.bielcik@fjfi.cvut.cz

  10. Leptons from HF decay at PHENIX PHENIX PRL, 98, 172301 (2007) p+p 200GeV/c PHENIX Preliminary • Electron spectrum is harder than muon spectrum, within errors they are consistent at intermediate pT • Systematically higher than FONLL calculation (up to factor ~ 4) • Integral e yield follows binary scaling, high pT strong suppression at central AuAu collisions jaroslav.bielcik@fjfi.cvut.cz

  11. STAR STAR high pT NP 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

  12. c dominant b dominant Heavy quarks in p+p from e+e- at PHENIX After subtraction of Cocktail - Fit to a*charm+ b*bottom (with PYTHIA shape) Extracted cross sections in good agreement with single e result. arXiv:0802.0050 jaroslav.bielcik@fjfi.cvut.cz

  13. Charm cross-section PRL 94 (2005) Total cross-section with large theoretical uncertainty. Both STAR and PHENIX are self-consistent  observation of binary scaling STAR results ~ 2 times larger than PHENIX Consistent with NLO calculation  however error bands are huge jaroslav.bielcik@fjfi.cvut.cz

  14. ENERGY LOSS/FLOW jaroslav.bielcik@fjfi.cvut.cz

  15. Elliptic flow v2 – NPE from HF decays PHENIX Run4 PRL, 98, 172301 (2007) • Non-zero elliptic flow for electron from heavy flavor decays • → indicatesnon-zero D v2,partonic level collective motion. • Strongly interact with the dense medium at early stage of HI collisions • Light flavor thermalization jaroslav.bielcik@fjfi.cvut.cz

  16. 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 Non-photonic electrons suppression similar to hadrons pT (NPE) < pT (D NPE) jaroslav.bielcik@fjfi.cvut.cz

  17. PRL 98, 172301 (2007) e± from heavy flavor Nuclear Modification Factor RAA • very similar to light hadron RAA • careful: • decay kinematics! • pT(e±) < pT(D) • intermediate pT • indication for quark mass hierarchy as expected for radiative energy loss • (Dokshitzer and Kharzeev, PLB 519(2001)199) • highest pT • RAA(e±) ~ RAA(p0) ~ RAA(h) • crucial to understand: • what is the bottom contribution? • ideal: • RAA of identified charm and bottom hadrons

  18. 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

  19. 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

  20. 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

  21. Bottom contribution to NPE (be)/(ce+be) • Difficult to interpret suppression without the knowledge of charm/bottom • Data shows non-zero B contribution • Good agreement among different analyses. • Data consistent with FONLL.

  22. Conclusions • Heavy flavor is an important tool to understand HI physics at RHIC • RHIC results are interesting and challenging charm cross section • Binary scaling in charm production produced in initial phase • Differences between STAR and PHENIX will be addressed • NLO is consistent with data non-photonic electrons • strong high-pT suppression in Au+Au large energy loss of c+b • heavy quark energy loss not understood • b relative contribution consistent with FONLL important b contribution • none zero charm flow is observed at RHIC energy does b also flow? large uncertainties jaroslav.bielcik@fjfi.cvut.cz

  23. 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

  24. 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)

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

  26. 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

  27. 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

  28. 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. jaroslav.bielcik@fjfi.cvut.cz

  29. 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

  30. 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

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

  32. jaroslav.bielcik@fjfi.cvut.cz

  33. 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

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