1. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 1  Motivation  STAR and electron ID  Analysis  Results: p+p, d+Au, and Au+Au at  s NN = 200 GeV  Summary Jaroslav Bielcik Yale University/BNL for the collaboration Centrality dependence of heavy flavor production from single electron measurements

2. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 2 STAR is one of the 4 experiments at RHIC in BNL on Long Island 545 Collaborators from 51 Institutions in 12 countries RHIC has been exploring nuclear matter at extreme conditions over the last few years STAR:

3. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 3 Phys. Rev. Lett. 91, 072304 (2003). Pedestal&flow subtracted Inclusive yields and back-to-back di-hadron correlations are very similar in p+p and d+Au collisions Both are strongly suppressed in central Au+Au collisions at 200 GeV STAR Light quarks sector Jet quenching Hadron suppression in central AuAu Large energy loss of light quarks in the formed nuclear matter

4. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 4 Heavy quarks sector c, b D, B 1) production 2) medium energy loss 3) fragmentation D,B spectra are affected by energy loss Can we learn something from the difference between heavy and light quarks? How do heavy quarks interact with the medium? – Thermalization in early stage of collision, suppression? 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 Effect of elastic energy loss for heavy quarks M.G.Mustafa Phys. Rev C 72 (2005)

5. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 5 Detecting charm/beauty via semileptonic D/B decays  Hadronic decay channels: D 0  K , D *  D 0 , D +/-  K   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) D0D0 Phys. Rev. Lett. 94 (2005) H.Zhang QM2005

6. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 6 Predictions of electron nuclear modification factor R AA  Beauty predicted to dominate above 4-5 GeV/c Single e- from NLO/FONLL scaled to M. Cacciari et al., hep-ph/0502203 electron suppression up to 2 large electron suppression of ~ 5 for c medium suppression of ~ 2.5 for c+b

7. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 7 STAR Detector and Data Sample Electrons in STAR:  TPC: tracking, PID |  |<1.3  =2   BEMC (tower, SMD): PID 0<  <1  =2   TOF patch 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 ) Processed: HighTower trigger:  Only events with high tower E T >3 GeV/c 2  Enhancement of high p T

8. Lake Louise 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 2 -10 4 electrons  Kp d hadronselectrons 8

9. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 9 Electron background  Inclusive electron spectra: Signal − Heavy quarks semi-leptonic decays Dominant background − Instrumental: - γ conversion – Hadronic decays: - Dalitz decays (π 0, η)  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 Background rejection efficiency central Au+Au M e+e- <0.14 GeV/c 2 red likesign

10. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 10 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%

11. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 11 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

12. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 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 Only c contribution would describe the R AA but not the p+p spectra

13. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 13 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  Strong suppression of non-photonic electrons has been observed in Au+Au increasing with centrality  R AA ~ 0.2-0.3 for p T > 3 GeV/c  suggests large energy loss for heavy quarks  Reconsidering of energy loss mechanism needed (incl. b suppression and centrality dependence)  Finalization of the data  e-e correlation (what happens with the other D?)  e-h correlation (heavy flavor tagged jets)

14. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 14 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

15. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 15 BACK UP SLIDES

16. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 16

17. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 17 Hadron contamination p/E method

18. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 18 Electron reconstruction efficiency AuAu200GeV the central collisions determined from electron embedding in real events the data are corrected for this effect

19. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 19 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

20. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 20 Two fake conversion points reconstructed (picking one closer to primary vertex )

21. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 21 Trigger bias MB/HT ratio (0-5%)

22. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 22 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!

23. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 23 Electron/Hadron ratio

24. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 24

25. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 25 P/E in momentum bins momentum [GeV/c] a.u.

26. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 26 dEdx for pt 6.5-7.0 GeV/c After EMC ID cuts the separation with dEdx is still good for high pT

27. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 27 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%

28. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 28 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

29. Lake Louise 2006 Jaroslav Bielcik, Yale/BNL 29 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