Xiaoyan Lin IOPP/UCLA For the STAR Collaboration

1. Azimuthal correlations between non-photonic electrons and charged hadrons in p+p collisions from STAR • Motivation • Electron identification • Photonic electron background • Electron-hadron correlation • Comparison to PYTHIA • Summary Xiaoyan Lin IOPP/UCLA For the STAR Collaboration Hard Probes 2006, Asilomar, June 9-16

2. STAR Heavy Quark RAA = Light Quark RAA Features in H-Q Measurements at RHIC Curves: S. Wicks, et al, nucl-th/0512076 Hard Probes 2006, Asilomar, June 9-16

3. Non-photonic electron V2 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! Curves: Greco, Ko, Rapp, PLB 595 (2004) 202 Hard Probes 2006, Asilomar, June 9-16

4. Quantitative understanding of features in heavy quark measurements requires Charm versus b quark contributions to non-photonic electrons ! Charm versus b quark contribution 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 Hard Probes 2006, Asilomar, June 9-16

5. Associated PT > 0.1 GeV/c 2.5<PT(trig)<3.5 GeV/c 3.5<PT(trig)<4.5 GeV/c 4.5<PT(trig)<5.5 GeV/c PYTHIA Simulation • 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 Δφbetween D and B mesons can help us to estimate relative B and D contributions to non-photonic electrons. Hard Probes 2006, Asilomar, June 9-16

6. Major Detectors Used Charm decay Bottom decay Signal: Non-photonic electron Background: Hadron Photonic electron Photon conversion π0 Dalitz decay η Dalitz decay kaon decay vector meson decays Data Sample: About 20M p+p collisions at sNN = 200 GeVin year 5 run. • Time Projection Chamber (TPC) • Electro-Magnetic Calorimeter (EMC) • Shower Maximum Detector (SMD) Hard Probes 2006, Asilomar, June 9-16

7. Electron Identification: dE/dx (-0.4σ, 3.0σ) • TPC can identify charged particles to some extent • Two orders of magnitude more hadrons than electrons • Additional information needed to identify electrons Hard Probes 2006, Asilomar, June 9-16

8. 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. Hard Probes 2006, Asilomar, June 9-16

9. 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. Hard Probes 2006, Asilomar, June 9-16

10. 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. Hard Probes 2006, Asilomar, June 9-16

11. Purity of Inclusive Electron Sample Hard Probes 2006, Asilomar, June 9-16

12. 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/c2 Hard Probes 2006, Asilomar, June 9-16

13. 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 Method to Extract the Signal of E-H Correlation • 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. • Δφnon-pho = Δφsemi-inc +Δφcombinatorics - (1/ε -1) (Δφopp-sign-NoPartner - Δφsame-sign-NoPartner) Hard Probes 2006, Asilomar, June 9-16

14. Associated PT > 0.1 GeV/c 2.5<PT(trig)<3.5 GeV/c 3.5<PT(trig)<4.5 GeV/c 4.5<PT(trig)<5.5 GeV/c Δφ Distributions Semi-inc Semi-inc Combinatorics Combinatorics Hard Probes 2006, Asilomar, June 9-16

15. 2.5<PT(trig)<3.5 GeV/c 3.5<PT(trig)<4.5 GeV/c 4.5<PT(trig)<5.5 GeV/c Δφ Distributions Opposite-Sign Opposite-Sign Same-Sign Same-Sign Hard Probes 2006, Asilomar, June 9-16

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

17. Assume the photonic b.g. reconstruction efficiency is 70% Comparison to PYTHIA Simulation • At high pT 4.5-5.5 GeV/c , the preliminary data indicates D contribution is larger than B. Hard Probes 2006, Asilomar, June 9-16

18. 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 PT ~ 5.5 GeV/c. • To quantitatively estimate B contribution, we need more study on the background, photonic electron reconstruction efficiency… Hard Probes 2006, Asilomar, June 9-16

19. Back up slides Hard Probes 2006, Asilomar, June 9-16

20. Photonic b.g. reco. efficiency uncertainty Hard Probes 2006, Asilomar, June 9-16

21. Photonic b.g. reco. efficiency uncertainty Hard Probes 2006, Asilomar, June 9-16

22. Photonic b.g. reco. efficiency uncertainty Hard Probes 2006, Asilomar, June 9-16

23. Width of near-side peak in PYTHIA simulation Hard Probes 2006, Asilomar, June 9-16

24. Hard Probes 2006, Asilomar, June 9-16