1. QM2005 BudapestJaroslav Bielcik  Motivation  STAR and electron ID  Analysis  Results: p+p, d+Au, and Au+Au at  s NN = 200 GeV  Summary Centrality dependence of heavy flavor production from single electron measurements Jaroslav Bielcik Yale University/BNL for the collaboration

2. QM2005 BudapestJaroslav Bielcik 2 Heavy quark production at RHIC c, b D, B 1) production 2) medium energy loss 3) fragmentation  Heavy quark energy loss is expected to be smaller because of dead cone  D,B spectra are affected by energy loss  Important test of transport properties of sQGP  Can we learn something from the difference between heavy and light quarks?  How do heavy quarks interact with the medium? – Thermalization, suppression? light (M.Djordjevic PRL 94 (2004)) ENERGY LOSS

3. QM2005 BudapestJaroslav Bielcik 3 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 (  0   e  e   )   0,  ’ Dalitz decays  ,  … decays (small)  K e3 decays (small) See H.Zhang talk 5c

4. QM2005 BudapestJaroslav Bielcik 4 Electrons and nuclear modification factor R AA  Beauty predicted to dominate above 4-5 GeV/c Single e- from NLO/FONLL prediction: electron suppression up to 2 scaled to prediction: large electron suppression of ~ 5 for c only medium suppression of ~ 2.5 for c+b M. Cacciari et al., hep-ph/0502203

5. QM2005 BudapestJaroslav Bielcik 5 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

6. QM2005 Budapest 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 4 -10 5 electrons  Kp d hadronselectrons

7. QM2005 BudapestJaroslav Bielcik 7 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

8. QM2005 BudapestJaroslav Bielcik 8 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%  Remaining problem: charge exchange reaction in EMC at high p T :  ±   0  (still under study)

9. QM2005 BudapestJaroslav Bielcik 9 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 See H.Zhang talk 5c

10. QM2005 BudapestJaroslav Bielcik 10 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

11. QM2005 BudapestJaroslav Bielcik 11 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 ~10GeV/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 of heavy quarks  Need more detailed theory (incl. b suppression and centrality dependence)  Still more data on tape …  More stat at central  e-e correlation (what happens with the other D?)  e-h correlation (heavy flavor tagged jets)

12. QM2005 BudapestJaroslav Bielcik 12 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

13. QM2005 BudapestJaroslav Bielcik 13 BACK UP SLIDES

14. QM2005 BudapestJaroslav Bielcik 14 Hadron contamination p/E method

15. QM2005 BudapestJaroslav Bielcik 15 Electron reconstruction efficiency AuAu200GeV the central collisions determined from electron embedding in real events the data are corrected for this effect

16. QM2005 BudapestJaroslav Bielcik 16 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

17. QM2005 BudapestJaroslav Bielcik 17 Two fake conversion points reconstructed (picking one closer to primary vertex )

18. QM2005 BudapestJaroslav Bielcik 18 Trigger bias MB/HT ratio (0-5%)

19. QM2005 BudapestJaroslav Bielcik 19 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!

20. QM2005 BudapestJaroslav Bielcik 20 Electron/Hadron ratio

21. QM2005 BudapestJaroslav Bielcik 21

22. QM2005 BudapestJaroslav Bielcik 22 P/E in momentum bins momentum [GeV/c] a.u.

23. QM2005 BudapestJaroslav Bielcik 23 dEdx for pt 6.5-7.0 GeV/c After EMC ID cuts the separation with dEdx is still good for high pT