1. Non-photonic electron production in STAR A. G. Knospe Yale University 9 April 2008

2. Heavy Flavor and the QGP Heavy quarks produced in initial hard scattering of partons –Dominant: gg  QQ –Production rates from pQCD –Sensitive to initial gluon distributions Heavy quark energy loss –Prediction: less than light quark energy loss (dead cone effect) –Sensitive to gluon densities in medium light M.Djordjevic PRL 94 (2004) ENERGY LOSS bottom parton medium slide 1 _ A. G. Knospe

3. Heavy Flavor Decays Must study heavy-flavor decay products Some studies reconstruct hadronic decays: i.e. D 0  K , D*  D 0 , D ±  K , D s ±  (S. Baumgart, A. Shabetai) I look at semileptonic decay modes: –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%) –   decay modes Heavy flavor decays expected to dominate non-photonic (single) e ± spectrum; b decays should dominate at high p T Photonic e ± background: –  conversions ( ,  e + e - ) – Dalitz decays of  0, ,  ’ – , , K e3 decays (small contributions) non-photonic e ± slide 2A. G. Knospe

4. Previous Results Combine e ± with oppositely charged tracks in same event; e ± is background if M inv < 150 MeV/c 2 Simulate background e ± from “cocktail” of measured sources ( ,  0, , etc.) Measure e ± with converter, extrapolate to 0 background To Remove Photonic e ± Background: Au+Au: 0-5% 40-80% p+pp+p d+Au Au+Au: 0-92% 0-10% 10-20% 20-40% 40-60% 60-92% p+pp+p 10-40% STAR: Non-photonic e ±, √s NN =200 GeV STAR: B. I. Abelev et al, Phys. Rev. Lett. 98 (2007) 192301 PHENIX: A. Adare et al, Phys. Rev. Lett. 98, 172301 (2007) PHENIX: Non-photonic e ±, √s NN =200 GeV slide 3A. G. Knospe

5. Nuclear Modification Factor PHENIX and STAR: R AA for Non-photonic e ± central Au+Au, √s NN =200 GeV Light Hadron R AA PHENIX: PRL 98 (2007) 172301 STAR: PRL 98 (2007) 192301 DVGL: Djordjevic, Phys. Lett. B 632 (2006) 81 BDMPS: Armesto, Phys. Lett. B 637 (2006) 362 slide 4 R AA for non-photonic e ± : PHENIX consistent with STAR Similar to light hadron R AA Kinematics: p T (e ± ) < p T (D) Use light hadron R AA to constrain parameters dN g /dy, q Models tend to under-predict suppression Models still being refined ^ A. G. Knospe

6. Nuclear Modification Factor PHENIX and STAR: R AA for Non-photonic e ± central Au+Au, √s NN =200 GeV Light Hadron R AA PHENIX: PRL 98 (2007) 172301 STAR: PRL 98 (2007) 192301 DVGL: Wicks, nucl-th/0512076 (2005) van Hees, Phys. Rev. C 73 034913 (2006) slide 4 R AA for non-photonic e ± : PHENIX consistent with STAR Similar to light hadron R AA Kinematics: p T (e ± ) < p T (D) Use light hadron R AA to constrain parameters dN g /dy, q Models tend to under-predict suppression Models still being refined A. G. Knospe ^

7. Nuclear Modification Factor PHENIX and STAR: R AA for Non-photonic e ± central Au+Au, √s NN =200 GeV Light Hadron R AA PHENIX: PRL 98 (2007) 172301 STAR: PRL 98 (2007) 192301 DVGL: Djordjevic, Phys. Lett. B 632 (2006) 81 slide 4 R AA for non-photonic e ± : PHENIX consistent with STAR Similar to light hadron R AA Kinematics: p T (e ± ) < p T (D) Use light hadron R AA to constrain parameters dN g /dy, q Models tend to under-predict suppression Models still being refined Do only c decays contribute? A. G. Knospe ^

8. B-decay Contribution STAR measures angular correlations of non- photonic e+ with hadrons –sensitive to relative contributions of D and B decays Measured B/(B+D) ratio consistent with FONLL –~ 40% at p T =5 GeV/c b-quarks should be considered in R AA calculation (cf. previous slide) Fractional Contribution of B slide 5 X. Lin, SQM 2007 A. G. Knospe

9. Non-photonic electrons in Cu + Cu, 200 GeV events

10. Cu+Cu: Event Selection Analyze STAR data from 2005 Cu+Cu 200 GeV run EMC High Tower Trigger: –At least one tower with E > 3.75 GeV –Enhances yields at high p T Start with: 34M minimum bias events and 3.7M high tower events Event Selection Cuts: –centrality 0-54% –primary vertex |z| < 20 cm –Normal e + yield Analyzed 10M min. bias events and 1.9M high tower events slide 6 preliminary A. G. Knospe

11. e ± Identification BEMC: –EMC = Towers + Shower Maximum Detector (SMD) –e ± in STAR EMC: p/E ≈ 1 –Use a loose cut: 0 < p/E < 2 –SMD used to identify e ± : showers better developed than h ± –Require hits (> 2 strips) in both the  and  planes of SMD –Mean BEMC Acceptance ~78% TPC: –3.5 < dE/dx < 5 keV/cm –Good dE/dx separation between e ± and  ± for p > 1.5 GeV/c –distance to primary vertex < 1.5 cm –0 <  < 0.7 –quality cuts EMC slide 7 preliminary A. G. Knospe

12. e ± Identification BEMC: –EMC = Towers + Shower Maximum Detector (SMD) –e ± in STAR EMC: p/E ≈ 1 –Use a loose cut: 0 < p/E < 2 –SMD used to identify e ± : showers better developed than h ± –Require hits (> 2 strips) in both the  and  planes of SMD –Mean BEMC Acceptance ~78% TPC: –3.5 < dE/dx < 5 keV/cm –Good dE/dx separation between e ± and  ± for p > 1.5 GeV/c –distance to primary vertex < 1.5 cm –0 <  < 0.7 –quality cuts slide 7A. G. Knospe hadronse±e± preliminary

13. e ± Identification BEMC: –EMC = Towers + Shower Maximum Detector (SMD) –e ± in STAR EMC: p/E ≈ 1 –Use a loose cut: 0 < p/E < 2 –SMD used to identify e ± : showers better developed than h ± –Require hits (> 2 strips) in both the  and  planes of SMD –Mean BEMC Acceptance ~78% TPC: –3.5 < dE/dx < 5 keV/cm –Good dE/dx separation between e ± and  ± for p > 1.5 GeV/c –distance to primary vertex < 1.5 cm –0 <  < 0.7 –quality cuts slide 7A. G. Knospe hadronse±e± SMD Clusters: preliminary

14. Corrections Embed simulated e ± tracks into real Cu+Cu events  = Reconstruction Efficiency: fraction of simulated e ± reconstructed and identified by cuts Correct for TPC energy loss separately Fit ln(dE/dx) projections in p slices purity (  P ): fraction of particles within dE/dx cut that are e ± –90-100%, decreasing w/ p T efficiency (  E ): fraction of e ± that fall within dE/dx cut –70-80% slide 8 preliminary from embedding Cu+Cu 200 GeV, MinBias, 0-54% A. G. Knospe preliminary e±e±  ± ± h±h± from real data 2 GeV/c < p < 3 GeV/c

15. Photonic e ± Background Dominant sources of photonic e ± : –Conversion (   e + e - ) –Dalitz decays (  0,   e + e - ) Photonic e ± from invariant mass cut: –e ± is paired with oppositely- charged tracks in same event Same-charge pairs give combinatorial background –Find pairs with dca < 1.5cm and M(e + e - ) < 150 MeV/c 2 –Photonic e ± yield: slide 9 Some ph. e ± not rejected –Embed simulated  0   e + e - decays + conversions into real Cu+Cu events –Background rejection efficiency (  B ): eff. to find true conversion partner (70-80%) preliminary black: e + e - pairs blue: comb. back. red=photonic invariant mass [GeV/c 2 ] 1.2 GeV/c < p T < 1.6 GeV/c A. G. Knospe

16. Spectra and R AA Apply corrections: Merge data sets Nuclear Modification Factor: –N binary = 82.2 for 0-54% –R AA ~ 0.6 - 0.7 for p T > 3 GeV/c slide 10 preliminary A. G. Knospe

17. R AA Comparisons Consistent with  ± R AA in Cu+Cu 200 GeV Non-photonic e ± Cu+Cu 200 GeV 0-54% Consistent with Au+Au 200 GeV data for similar N part R AA for  ±, Cu+Cu 200 GeV R AA for non-photonic e ± slide 11 * R. Hollis, WWND 2007 STAR: PRL 98 (2007) 192301 PHENIX: PRL 98 (2007) 172301 A. G. Knospe

18. Summary Non-photonic e ± are proxies for heavy quarks Found the non-photonic e ± spectra in Cu+Cu 200 GeV data –Particle ID in TPC, BEMC, BSMD –Remove photonic e ± with invariant mass cut: M(e + e - ) < 150MeV/c 2 Nuclear Modification Factor 0.6 - 0.7 for p T > 3 GeV/c, centrality 0-54% –Consistent with  ± R AA in Cu+Cu 200 GeV –Consistent with non- photonic e ± R AA in Au+Au 200 GeV at similar N part slide 12A. G. Knospe

19. The Future Coming soon: find yields and R AA in three centrality bins Paper on D-mesons and non-photonic e ± in Cu+Cu 200 GeV: S. Baumgart, A. G. Knospe, and A. Shabetai slide 13 Thank you! Are there any questions? A. G. Knospe

20. Additional Material

21. Comparisons to PQCD FONLL describes shape of non-photonic e ± spectra PHENIX spectrum < STAR by factor ~2 FONLL predition < STAR by factor ~4-5 differences constant in p T Non-photonic e ± in p+p, 200 GeV New PQCD calculations: –Error bars on total  cc larger than earlier calculations –STAR data consistent with new upper limit (Prediction II) Total Charm Cross-Section A. G. Knospe