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

2. jaroslav.bielcik@fjfi.cvut.cz2 Outline Motivation for heavy flavor physics Spectra: – Charm mesons: D 0 – 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)

3. jaroslav.bielcik@fjfi.cvut.cz3 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 pQCD M. 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 extract properties of the medium parton hot and dense medium light M.Djordjevic PRL 94 (2004) ENERGY LOSS dead-cone effect: Dokshitzer and Kharzeev, PLB 519, 199 (2001)

4. jaroslav.bielcik@fjfi.cvut.cz4 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%)

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

6. SPECTRA jaroslav.bielcik@fjfi.cvut.cz6

7. 7 STAR Preliminary Direct D-meson reconstruction at STAR D0D0 Phys. Rev. Lett. 94 (2005) K  invariant mass distribution in d+Au, Au+Au minbias, Cu+Cu minbias at 200 GeV collisions No displaced vertex used => only p T <3.3 GeV/c jaroslav.bielcik@fjfi.cvut.cz

8. 8 PHENIX Preliminary Year5 pp 200 GeV Direct D-meson reconstruction at PHENIX p+p 200 GeV/c:  D 0  K +  -  0 decay channel  0 identified via  0   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. 9 Leptons from HF decay at STAR STAR Preliminary STAR charm cross section: combined fit of muons, D 0 and low p T electrons  90% of total kinematic range covered New Cu+Cu D 0 spectrum agree with Au+Au after number of binary scaled Low p T muon constrains charm cross-section jaroslav.bielcik@fjfi.cvut.cz

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

11. 11 High-tower EMC trigger => high p T electrons FONLL scaled by ~5, describes shape of p+p spectra well suggesting bottom contribution STAR high p T NP electrons STAR Phys. Rev. Lett. 98 (2007) 192301 STAR Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys. Rev. Lett. 97 (2006) 252002 jaroslav.bielcik@fjfi.cvut.cz

12. 12 Heavy quarks in p+p from e + e - at PHENIX c dominant b dominant 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. 13 Charm cross-section PRL 94 (2005) 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 Total cross-section with large theoretical uncertainty.

14. ENERGY LOSS/FLOW jaroslav.bielcik@fjfi.cvut.cz14

15. 15 Elliptic flow v 2 – NPE from HF decays Non-zero elliptic flow for electron from heavy flavor decays → indicates non-zero D v 2, partonic level collective motion. Strongly interact with the dense medium at early stage of HI collisions Light flavor thermalization PHENIX Run4 PRL, 98, 172301 (2007) jaroslav.bielcik@fjfi.cvut.cz

16. 16 d+Au: no suppression expected slight enhancement expected (Cronin effect) Peripheral Au+Au: no suppression expected Semi-Central Au+Au: very little suppression expected R AA from d+Au to central Au+Au STAR hadrons p T > 6 GeV/c Central Au+Au: little suppression expected ?! Nuclear modification factor STAR Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301 Non-photonic electrons suppression similar to hadrons p T (NPE) < p T (D  NPE)

17. PRL 98, 172301 (2007) e ± from heavy flavor Nuclear Modification Factor R AA l very similar to light hadron R AA l careful: –decay kinematics! –p T (e ± ) < p T (D) l intermediate p T –indication for quark mass hierarchy as expected for radiative energy loss (Dokshitzer and Kharzeev, PLB 519(2001)199) l highest p T –R AA (e ± ) ~ R AA (  0 ) ~ R AA (  ) l crucial to understand: what is the bottom contribution? l ideal: R AA of identified charm and bottom hadrons

18. jaroslav.bielcik@fjfi.cvut.cz18 Radiative energy loss Radiative energy loss alone in medium with reasonable parameters does not describe the data Djordjevic, Phys. Lett. B632 81 (2006) Armesto, Phys. Lett. B637 362 (2006) What are the other sources of energy loss ? parameters of medium in models extracted from hadron data STAR Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301

19. jaroslav.bielcik@fjfi.cvut.cz19 Role of collisional energy loss Wicks, nucl-th/0512076 van Hess, Phys. Rev. C73 034913 (2006) Collisional/elastic energy loss may be important for heavy quarks Still not good agreement at high-pT STAR Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301

20. jaroslav.bielcik@fjfi.cvut.cz20 Charm alone? Since the suppression of b quark electrons is smaller – charm alone agrees better What is b contribution? STAR Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301

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

22. jaroslav.bielcik@fjfi.cvut.cz22 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-p T 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

23. PRL 98, 172301 (2007) l at  B = 0 l  + P = Ts l then l  /s = (1.3-2.0)/4  l transport models l Rapp & van Hees (PRC 71, 034907 (2005)) –diffusion coefficient required for simultaneous fit of R AA and v 2 –D HQ x2  T ~ 4-6 Estimating  /s l Moore & Teaney (PRC 71, 064904 (2005)) –difficulties to describe R AA and v 2 simultaneously –calculate perturbatively (and argue that plausible also non-perturbatively) –D HQ / (  /(  +P)) ~ 6 (for N f = 3)

24. S. Gavin and M. Abdel-Aziz: PRL 97:162302, 2006 p T fluctuations STAR Comparison with other estimates R. Lacey et al.: PRL 98:092301, 2007 v 2 PHENIX & STAR H.-J. Drescher et al.: arXiv:0704.3553 v 2 PHOBOS conjectured quantum limit l estimates of  /s based on flow and fluctuation data l indicate small value as well l close to conjectured limit l significantly below  /s of helium (  s ~ 9)

25. Charm ~ y jaroslav.bielcik@fjfi.cvut.cz25

26. jaroslav.bielcik@fjfi.cvut.cz26 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

27. jaroslav.bielcik@fjfi.cvut.cz27 Low-p T (p T < 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 m inv 2 (GeV 2 /c 4 )   0.17 < p T < 0.21 GeV/c 0-12% Au+Au Muon measurement TPC+TOF Inclusive   from charm  from  / K (simu.) Signal+bg. fit to data (STAR), Hard Probes 2006 m 2 =(p/  /  ) 2

28. jaroslav.bielcik@fjfi.cvut.cz28 Conversion from dN/dy to Cross-Section p+p inelastic cross section conversion to full rapidity ratio from e + e - collider data number of binary collisions *Systematic error measurement for dN/dy in progress.

29. jaroslav.bielcik@fjfi.cvut.cz29 hadrons electrons 1.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 2.EMC : a)Tower E ⇒ p/E~1 for e - b)Shower Max Detector Hadrons/Electron shower develop different shape 85-90% purity of electrons (p T dependent) electrons  Kp d all p>1.5 GeV/c 2 p/E SMD Electron ID in STAR – EMC

30. jaroslav.bielcik@fjfi.cvut.cz30 Photonic electrons background  Background : Mainly from  conv and    Dalitz  Rejection strategy: For every electron candidate  Combinations with all TPC electron candidates  M e+e- <0.14 GeV/c 2 flagged photonic  Correct for primary electrons misidentified as background  Correct for background rejection efficiency ~50-60% for central Au+Au Inclusive/Photonic:  Excess over photonic electrons observed for all system and centralities => non-photonic signal

31. jaroslav.bielcik@fjfi.cvut.cz31  CC : comparison with other measurements

32. jaroslav.bielcik@fjfi.cvut.cz32

33. Power-law function with parameters dN/dy, and n to describe the D 0 spectrum D 0, e ,   combined fit Generate D 0  e decay kinematics according to the above parameters Vary (dN/dy,, n) to get the min.  2 by comparing power-law to D 0 data and the decayed e shape to e  and   data Advantage: D 0 and   constrain low p T e  constrains higher p T Spectra difference between e  and   ~5% (included into sys. error) Combined Fit