1. Xiaoyan LinHard Probes 2006, Asilomar, June 9-161 Azimuthal correlations between non-photonic electrons and charged hadrons in p+p collisions from STAR Xiaoyan Lin IOPP/UCLA For the STAR Collaboration  Motivation  Electron identification  Photonic electron background  Electron-hadron correlation  Comparison to PYTHIA  Summary

2. Xiaoyan LinHard Probes 2006, Asilomar, June 9-162 STAR Features in H-Q Measurements at RHIC Heavy Quark R AA = Light Quark R AA Curves: S. Wicks, et al, nucl-th/0512076

3. Xiaoyan LinHard Probes 2006, Asilomar, June 9-163 Features in H-Q Measurements at RHIC Heavy Meson Flows ! Note the decay kinematics of D and B mesons are different! Electrons from B decays cannot follow the B meson momentum direction as good as electrons from D decays! Non-photonic electron V 2 Curves: Greco, Ko, Rapp, PLB 595 (2004) 202

4. Xiaoyan LinHard Probes 2006, Asilomar, June 9-164 Charm versus b quark contribution Quantitative understanding of features in heavy quark measurements requires Charm versus b quark contributions to non-photonic electrons ! Such information should be best obtained from direct measurement of hadronic decays of charm and bottom mesons. This motivates the STAR and PHENIX vertex detector upgrade! See Dr. Nu Xu’s talk. Non-photonic electron and hadron correlations can help to estimate the C and B contribution ! X. Lin hep-ph/0602067

5. Xiaoyan LinHard Probes 2006, Asilomar, June 9-165 Significant difference between D decays and B decays in the near-side correlations. The difference is largely due to decay kinematics, not the production dynamics. The large difference in the near-side Δφ between D and B mesons can help us to estimate relative B and D contributions to non-photonic electrons. PYTHIA Simulation 2.5<P T (trig)<3.5 GeV/c3.5<P T (trig)<4.5 GeV/c4.5<P T (trig)<5.5 GeV/c Associated P T > 0.1 GeV/c

6. Xiaoyan LinHard Probes 2006, Asilomar, June 9-166 Signal: Non-photonic electron Background: Hadron Photonic electron Major Detectors Used Time Projection Chamber (TPC) Electro-Magnetic Calorimeter (EMC) Shower Maximum Detector (SMD) Charm decay Bottom decay Photon conversion π 0 Dalitz decay η Dalitz decay kaon decay vector meson decays Data Sample:  s NN = 200 GeV in year 5 run. About 20M p+p collisions at  s NN = 200 GeV in year 5 run.

7. Xiaoyan LinHard Probes 2006, Asilomar, June 9-167 Electron Identification: dE/dx TPC can identify charged particles to some extent Two orders of magnitude more hadrons than electrons Additional information needed to identify electrons (-0.4σ, 3.0σ)

8. Xiaoyan LinHard Probes 2006, Asilomar, June 9-168 Electron Identification: P/E P is measured by TPC. E is the sum of the associated BEMC points’ energy measured by BEMC. Electrons will deposit almost all of their energy in the BEMC towers. 0.3 < P/E <1.5 was used to keep electrons and reject hadrons.

9. Xiaoyan LinHard Probes 2006, Asilomar, June 9-169 Electron Identification: Shower Size Number of SMD hits per shower indicates shower size. Electrons have larger number of BSMD hits than those for hadrons. Electron candidates have to satisfy Number of BSMD hits > 1.

10. Xiaoyan LinHard Probes 2006, Asilomar, June 9-1610 Electron Identification: Projection Distance -3σ < ZDist < 3σ and -3σ < PhiDist < 3σ were set to remove lots of random associations between TPC tracks and BEMC points.

11. Xiaoyan LinHard Probes 2006, Asilomar, June 9-1611 Purity of Inclusive Electron Sample electron p T purity 2.5-3.5 GeV/c99.99% 3.5-4.5 GeV/c99.34% 4.5-5.5 GeV/c99.14%

12. Xiaoyan LinHard Probes 2006, Asilomar, June 9-1612 Photonic Background The combinatorial background is small. Reconstructed photonic electron is the subtraction. Photonic electron is the reconstructed-photonic/eff eff ~ 60-70% from simulation for pp year 4. Still working on progress for pp year 5. M<100 MeV/c 2

13. Xiaoyan LinHard Probes 2006, Asilomar, June 9-1613 Method to Extract the Signal of E-H Correlation Start with Semi-Inclusive electron sample. If tracks pass the electron identification cuts, then they are inclusive electrons. In this inclusive electron sample we throw away those electrons which satisfy the photon conversion condition. The sample remaining is called semi-inclusive electrons. Semi-Inclusive = non-phtonic + not reconstructed-photonic - combinatorics Combinatorics can be estimated by Same-Sign. Not reco-photonic = photonic – reco-photonic = (1/eff – 1) (reco-photonic). For the e-h correlation analysis, we have to remove the photonic partner of the reco-photonic. Δφ non-pho = Δφ semi-inc + Δφ combinatorics - (1/ε -1) (Δφ opp-sign- NoPartner - Δφ same-sign-NoPartner )

14. Xiaoyan LinHard Probes 2006, Asilomar, June 9-1614 Δφ Distributions 2.5<P T (trig)<3.5 GeV/c3.5<P T (trig)<4.5 GeV/c4.5<P T (trig)<5.5 GeV/c Associated P T > 0.1 GeV/c Semi-inc Combinatorics

15. Xiaoyan LinHard Probes 2006, Asilomar, June 9-1615 Δφ Distributions 2.5<P T (trig)<3.5 GeV/c3.5<P T (trig)<4.5 GeV/c4.5<P T (trig)<5.5 GeV/c Opposite-Sign Same-Sign

16. Xiaoyan LinHard Probes 2006, Asilomar, June 9-1616 Comparison to PYTHIA Simulation Assume the photonic b.g. reconstruction efficiency is 70% At low p T 2.5 - 3.5 GeV/c, the preliminary data indicates D contribution is dominate.

17. Xiaoyan LinHard Probes 2006, Asilomar, June 9-1617 Comparison to PYTHIA Simulation Assume the photonic b.g. reconstruction efficiency is 70% At high p T 4.5-5.5 GeV/c, the preliminary data indicates D contribution is larger than B.

18. Xiaoyan LinHard Probes 2006, Asilomar, June 9-1618 Summary  We find that non-photonic electron and hadron correlations are sensitive to D and B contributions.  The preliminary data indicates D contribution is larger than B contribution up to P T ~ 5.5 GeV/c.  To quantitatively estimate B contribution, we need more study on the background, photonic electron reconstruction efficiency…

19. Xiaoyan LinHard Probes 2006, Asilomar, June 9-1619 Back up slides

20. Xiaoyan LinHard Probes 2006, Asilomar, June 9-1620 Photonic b.g. reco. efficiency uncertainty

21. Xiaoyan LinHard Probes 2006, Asilomar, June 9-1621 Photonic b.g. reco. efficiency uncertainty

22. Xiaoyan LinHard Probes 2006, Asilomar, June 9-1622 Photonic b.g. reco. efficiency uncertainty

23. Xiaoyan LinHard Probes 2006, Asilomar, June 9-1623 Width of near-side peak in PYTHIA simulation electron Pt (GeV/c)2.5-3.53.5-4.54.5-4.5 All hadrons e from D decays 0.359 ± 0.003 0.29 ± 0.003 0.2532 ± 0.0042 Hadrons from D decays e from D decays 0.3792 ± 0.0096 0.2992 ± 0.0098 0.2457 ± 0.0106

24. Xiaoyan LinHard Probes 2006, Asilomar, June 9-1624