1. Hot Quarks 2006 jaroslav.bielcik@yale.edu 1 Suppression of high-p T non-photonic electrons in Au+Au collisions at √s NN = 200 GeV HOT QUARKS 2006 Jaroslav Bielcik Yale University/BNL

2. Hot Quarks 2006 jaroslav.bielcik@yale.edu 2 Inclusive yields are strongly suppressed in central Au+Au collisions at 200 GeV Hadron suppression in central AuAu STAR Large energy loss of light quarks in the formed nuclear matter Energy loss depends on properties of medium (gluon densities, size) depends on properties of “probe” (color charge, mass) Probing the medium with heavy quarks => need to measure heavy quark mesons p+p (d+Au) and Au+Au

3. Hot Quarks 2006 jaroslav.bielcik@yale.edu 3 Measuring charm and beauty  Hadronic decay channels: D 0  K , D *  D 0 , D +/-  K  (Haibin’s talk)  Non-photonic electrons:  Semileptonic channels:  c  e + + anything (B.R.: 9.6%) –D 0  e + + anything(B.R.: 6.87%) –D   e  + anything(B.R.: 17.2%)  b  e + + anything(B.R.: 10.9%) –B   e  + anything(B.R.: 10.2%)  Drell-Yan (small contribution for p T < 10 GeV/c)  Photonic electron background:   conversions (     e + e - )     ’ Dalitz decays   … decays (small)  K e3 decays (small)

4. Hot Quarks 2006 jaroslav.bielcik@yale.edu 4 Heavy flavor electrons from FONLL  Beauty predicted to dominate above 4-5 GeV/c heavy flavor e- from FONLL scaled to Cacciari, Nason, Vogt, Phys.Rev.Lett 95 (2005) Large uncertainty on b/c crossing point in p T : from scales/masses variation it changes from 3 to 9 GeV/c

5. Hot Quarks 2006 jaroslav.bielcik@yale.edu 5 Energy loss of heavy quarks D, B (electrons) 1) production in hard scattering c, b 2) quark energy loss 3) fragmentation D,B (electrons) spectra are affected by energy loss light M.Djordjevic PRL 94 (2004) ENERGY LOSS Heavy quark has less dE/dx due to suppression of small angle gluon radiation “Dead Cone” effect Y. Dokshitzer & D. Kharzeev PLB 519(2001)199 Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003 Effect of collisional energy loss for heavy quarks M.G.Mustafa Phys. Rev C 72 (2005) M.Djordjevic nucl-th/0630066

6. Hot Quarks 2006 jaroslav.bielcik@yale.edu 6 Heavy quark energy loss BDMPS case BDMPS: Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003 Dainese, Loizides, Paic, EPJC 38 (2005) 461. Model: pQCD + E loss probability (quenching weights) + Glauber collision geometry  Density ( ) “tuned” to match R AA in central Au-Au at 200 GeV 0.4 0.1 hep-ph/0510284 0.2 0.3 light heavy =14 GeV 2 /fm R AA ~ 0.2 light mesons R AA ~ 0.4 for electrons from c+b

7. Hot Quarks 2006 jaroslav.bielcik@yale.edu 7 Heavy quark energy loss DGLV case Wicks et al nucl-th/0512076 ignore the data for the moment DGLV: Djordjevic, Guylassy Nucl.Phys. A 733, 265 (2004) dNg/dy=1000 gluon density of produced matter + Elastic energy loss ( Wicks et al nucl-th/0512076 ) light heavy RAA ~ 0.2 light mesons RAA ~ 0.4-0.6 for electrons from c+b Djordjevic et al. Phys.Lett B 632, 81 (2006)

8. Hot Quarks 2006 jaroslav.bielcik@yale.edu 8 STAR Detector and Data Sample Electrons in STAR:  TPC: tracking, PID |  |<1.3  =2   BEMC (tower, SMD): PID 0<  <1  =2   TOF patch (Haibin talk) Run2003/2004 min. bias. 6.7M events with half field high tower trigger 2.6M events with full field (45% of all) 10% central 4.2M events (15% of all ) Preliminary results from: HighTower trigger:  Only events with high tower E T >3 GeV/c 2  Enhancement of high p T

9. Hot Quarks 2006 hadrons electrons Electron ID in STAR – EMC 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 Use # hits cuts 85-90% purity of electrons (p T dependent) h discrimination power ~ 10 3 -10 4 electrons  Kp d

10. Hot Quarks 2006 jaroslav.bielcik@yale.edu 10 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 AuAu M e+e- <0.14 GeV/c 2 red likesign  Excess over photonic electrons observed for all system and centralities => non-photonic signal Inclusive/Photonic:

11. Hot Quarks 2006 jaroslav.bielcik@yale.edu 11 STAR non-photonic electron spectra pp, dAu, AuAu  s NN = 200 GeV  pp, dAu: up to 10 GeV/c  AuAu: 0-5%, 10-40%, 40-80% up to 8 GeV/c  Photonic electrons subtracted  Corrected for 10-15% hadron contamination  Beauty is expected to give an important contribution above 5 GeV/c

12. Hot Quarks 2006 jaroslav.bielcik@yale.edu 12 R AA nuclear modification factor Suppression up to ~ 0.5-0.6 observed in 40-80% centrality ~ 0.5 -0.6 in centrality 10-40% Strong suppression up to ~ 0.2 observed at high p T in 0-5% Maximum of suppression at p T ~ 5-6 GeV/c Theories currently do not describe the data well Only c contribution would be consistent with the R AA but not the p+p spectra Armesto et al. hep-th/0511257 van Hess et al. Phys. Rev. C 73, 034913 (2006) Wicks et al. (DVGL) hep-th/0512076

13. Hot Quarks 2006 jaroslav.bielcik@yale.edu 13 RECENT ELECTRON R AA BY D. TEANEY D.Teaney (Moriond 2006)  Input: spectrum of c+b from Cacciari et. al.  Weak coupling  Boltzmann-Langevin Model Phys.Rev.C71;064904 (2005)  Only collisional energy loss  Neglect radiative energy loss (  v<6)  Hadronization: according to measured fragmentation functions diffusion coefficient D=3/2  T corresponds to dN g /dy~2000

14. Hot Quarks 2006 jaroslav.bielcik@yale.edu 14 Large electrons suppression is a PUZZLE  Large suppression => large dE/dx of heavy quarks (NOT EXPECTED) Maybe higher at pT?  Where b starts to play a role?  Elastic energy loss? Important, helps, but not enough! Not enough, R AA saturates!  Large dN g /dy~ 3500, q ~14 GeV 2 /fm ? ^ Armesto et al. hep-ph/0511257 The low end of c-b overlap The high end of c-b overlap Wicks et al nucl-th/0512076  Recent study on 3 body cqq elastic scattering in QGP No beauty included! Liu&Ko nucl-th/0603004

15. Hot Quarks 2006 jaroslav.bielcik@yale.edu 15 Summary  Non-photonic electrons from heavy flavor decays were measured in  s = 200 GeV p+p, d+Au and Au+Au collisions by STAR up to p T ~10 GeV/c Expected to have contribution from both charm and beauty  Strong suppression of non-photonic electrons has been observed in Au+Au, increasing with centrality Suggests large energy loss for heavy quarks ( R AA similar to light quarks )  Theoretical attempts to explain it seem to fail if both b+c are included What is the contribution of b? Are there other/different contributions to energy loss?  It is desirable to separate contribution b+c experimentally detector upgrades (displaced vertex) e-h correlations

16. Hot Quarks 2006 jaroslav.bielcik@yale.edu 16 Argonne National Laboratory Institute of High Energy Physics - Beijing University of Bern University of Birmingham Brookhaven National Laboratory California Institute of Technology University of California, Berkeley University of California - Davis University of California - Los Angeles Carnegie Mellon University Creighton University Nuclear Physics Inst., Academy of Sciences Laboratory of High Energy Physics - Dubna Particle Physics Laboratory - Dubna University of Frankfurt Institute of Physics. Bhubaneswar Indian Institute of Technology. Mumbai Indiana University Cyclotron Facility Institut de Recherches Subatomiques de Strasbourg University of Jammu Kent State University Institute of Modern Physics. Lanzhou Lawrence Berkeley National Laboratory Massachusetts Institute of Technology Max-Planck-Institut fuer Physics Michigan State University Moscow Engineering Physics Institute City College of New York NIKHEF Ohio State University Panjab University Pennsylvania State University Institute of High Energy Physics - Protvino Purdue University Pusan University University of Rajasthan Rice University Instituto de Fisica da Universidade de Sao Paulo University of Science and Technology of China - USTC Shanghai Institue of Applied Physics - SINAP SUBATECH Texas A&M University University of Texas - Austin Tsinghua University Valparaiso University Variable Energy Cyclotron Centre. Kolkata Warsaw University of Technology University of Washington Wayne State University Institute of Particle Physics Yale University University of Zagreb 545 Collaborators from 51 Institutions in 12 countries STAR Collaboration

17. Hot Quarks 2006 hadrons electrons Electron ID in STAR – EMC 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 b)Shower Max Detector (SMD) Hadrons/Electron shower develop different shape Use # hits cuts 85-90% purity of electrons (p T dependent) h discrimination power ~ 10 3 -10 4 electrons  Kp d hadronselectrons

18. Hot Quarks 2006 jaroslav.bielcik@yale.edu 18 Charm Total Cross Section 1.13  0.09(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 per NN interaction Charm total cross section follows roughly Nbin scaling from d+Au to Au+Au considering errors Indication of charm production in initial collisions

19. Hot Quarks 2006 jaroslav.bielcik@yale.edu 19 What is v2? Non-central Au-Au collisions  azimuthally anisotropic source of matter in coordinate space  azimuthally anisotropic (isotropic) of particles in momentum space, given enough particle interactions  Non-zero (zero) v2 v2 is built up at the early stage of the collision so it is a nice probe of the hot and dense medium created at RHIC energy!

20. Hot Quarks 2006 jaroslav.bielcik@yale.edu 20 123 4 5 1: inclusive 2: OSLM 3: SSLM 4: 2-3 5: 1-(2-3)/eff OSLM: Opposite Sign Low Invariant Mass; SSLM: Same Sign Low Invariant Mass Charm electron v2 determination AFTER SUBTRACTING BACKGOUND CONTRIBUTION – LARGE SYSTEMATIC ERRORS

21. Hot Quarks 2006 jaroslav.bielcik@yale.edu 21 The detector material in STAR caused too much photonic background, which caused huge systematic and statistical uncertainties. Our result is not sensitive enough to make any conclusion about heavy quark v2 so far. Electron v2 with new method – large systematic errors

22. Hot Quarks 2006 jaroslav.bielcik@yale.edu 22 Charm energy loss Strong suppression observed! Indicates charm energy loss in medium. For D 0 R AA, stat. error only. STAR Preliminary

23. Hot Quarks 2006 jaroslav.bielcik@yale.edu 23 Hadron contamination p/E method

24. Hot Quarks 2006 jaroslav.bielcik@yale.edu 24 Electron reconstruction efficiency AuAu200GeV the central collisions determined from electron embedding in real events the data are corrected for this effect

25. Hot Quarks 2006 jaroslav.bielcik@yale.edu 25 Part of the primary electrons is flaged as background AuAu200GeV the central collisions determined from electron embedding in real events the data are corrected for this effect

26. Hot Quarks 2006 jaroslav.bielcik@yale.edu 26 Two fake conversion points reconstructed (picking one closer to primary vertex )

27. Hot Quarks 2006 jaroslav.bielcik@yale.edu 27 Trigger bias MB/HT ratio (0-5%)

28. Hot Quarks 2006 jaroslav.bielcik@yale.edu 28 Dalitz Decays:     e  e  versus     e  e  The background efficiency for Dalitz electrons is evaluated by weighting with the  0 distribution but should be weighted by the true    distribution. Comparing the spectra of this both cases normalized to give the same integral for p T >1 GeV/c (cut-off for electron spectra) we see almost no deviation. The effect of under/over correction is on the few percent level!

29. Hot Quarks 2006 jaroslav.bielcik@yale.edu 29 Electron/Hadron ratio

30. Hot Quarks 2006 jaroslav.bielcik@yale.edu 30

31. Hot Quarks 2006 jaroslav.bielcik@yale.edu 31 P/E in momentum bins momentum [GeV/c] a.u.

32. Hot Quarks 2006 jaroslav.bielcik@yale.edu 32 dEdx for pt bins

33. Hot Quarks 2006 jaroslav.bielcik@yale.edu 33 Inclusive electron spectra AuAu  s NN = 200 GeV  High tower trigger allows STAR to extend electron spectra up to 10 GeV/c  3 centrality bins: 0-5% 10-40% 40-80%  Corrected for hadron contamination ~10-15%

34. Hot Quarks 2006 jaroslav.bielcik@yale.edu 34 STAR non-photonic electron spectra pp,dAu,AuAu  s NN = 200 GeV  Photonic electrons subtracted  Excess over photonic electrons observed  Consistent with STAR TOF spectra Beauty is expected to give an important contribution above 5 GeV/c

35. Hot Quarks 2006 jaroslav.bielcik@yale.edu 35 R AA nuclear modification factor Suppression up to ~ 0.4-0.6 observed in 40-80% centrality ~ 0.3 -0.4 in centrality 10-40% Strong suppression up to ~ 0.2 observed at high p T in 0-5% Maximum of suppression at p T ~ 5-6 GeV/c

36. Hot Quarks 2006 jaroslav.bielcik@yale.edu 36 Inclusive electron spectra  s NN = 200 GeV TOF electrons STAR Preliminary  Excess of electrons over photonic background in all centralities and systems  Corrected for 10-15% hadron contamination

37. Hot Quarks 2006 jaroslav.bielcik@yale.edu 37 STAR non-photonic electron spectra pp,dAu,AuAu  s NN = 200 GeV  Photonic electrons subtracted  Consistent with STAR TOF spectra  Consistent with PHENIX Beauty is expected to give an important contribution above 5 GeV/c STAR Preliminary

38. Hot Quarks 2006 jaroslav.bielcik@yale.edu 38

39. Hot Quarks 2006 jaroslav.bielcik@yale.edu 39 Hadron suppression

40. Hot Quarks 2006 jaroslav.bielcik@yale.edu 40 Au+Au Systematical uncertainity d+Au and p+p40-80%10-40%0-5%Notes electron id and track efficiency (including dE/dx cut efficiency) 0.25 + 0.05 (2 GeV/c) 0.50 + 0.05 (8 GeV/c) 0.16 + 0.05 (2 GeV/c) 0.47 + 0.05 (8 GeV/c) 0.14 + 0.05 (2 GeV/c) 0.47 + 0.05 (8 GeV/c) 0.13 + 0.05 (2 GeV/c) 0.45 + 0.05 (8 GeV/c) Obtained from embedding, using different cluster finder and electron cuts. See a plot here of the efficiency variations for 0-5% most central Au-Au See a plot here of the efficiency variations for 0-5% most central Au-Au Hadronic contamination (0.50 + 0.03)% (2 GeV/c) (20 + 4)% (8 GeV/c) (2.0 + 0.1)% (2 GeV/c) (20 + 4)% (8 GeV/c) (2.0 + 0.1)% (2 GeV/c) (22 + 5)% (8 GeV/c) Obtained from changing dE/dx fit parameters Background finding efficiency 0.65 + 0.060.67 + 0.060.62 + 0.060.56 + 0.06 From different photon weigth functions and systematical differences between Alex/Jaro/Yifei/Weijiang and Frank analysis Bremsstrahlung 0.86 + 0.14 (2 GeV/c) 1.05 + 0.05 (8 GeV/c) 0.9 + 0.1 (2 GeV/c) 1.1 + 0.1 (8 GeV/c) Use the size of the correction as suggested by Jamie Acceptance0.84 + 0.05 0.75 + 0.15 from the EMC database tables Click here for details Click here for details Trigger bias uncertainty8%6% 5% From the trigger bias fit parameters Normalization uncertainty14% for p+pOverall normalization for p+p

41. Hot Quarks 2006 jaroslav.bielcik@yale.edu 41 for the collaboration