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Xiaoyan Lin 林晓燕 (for the STAR Collaboration) Central China Normal University Wuhan, P.R. China

Study B and D Contributions to Non-photonic Electrons via Azimuthal Correlations between Non- Photonic Electrons and Charged Hadrons. Xiaoyan Lin 林晓燕 (for the STAR Collaboration) Central China Normal University Wuhan, P.R. China. Outline. Motivation Data analysis

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Xiaoyan Lin 林晓燕 (for the STAR Collaboration) Central China Normal University Wuhan, P.R. China

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  1. Study B and D Contributions to Non-photonic Electrons via Azimuthal Correlations between Non-Photonic Electrons and Charged Hadrons Xiaoyan Lin 林晓燕 (for the STAR Collaboration) Central China Normal University Wuhan, P.R. China Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  2. Outline • Motivation • Data analysis ---- Electron identification ---- Photonic electron background ---- Electron-hadron correlations • Preliminary results of B/(B+D) • Summary Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  3. Features in Heavy Quark Measurements at RHIC----Non-Photonic Electron RAA • Heavy quark RAA has the similar magnitude as light quark RAA. • The high pT region non-photonic electron RAA is surprising ! • Where is the bottom contribution? Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  4. Features in Heavy Quark Measurements at RHIC----Non-Photonic Electron v2 • Reduction of v2 at pT > 2 GeV/c. Bottom contribution?? • The decay kinematics of D and B mesons are different! • The same D and B v2 can lead to very different non-photonic electron v2 ! Y. Zhang, hep-ph/0611182 PYTHIA Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  5. B and D Contributions to Electrons • Quantitative understanding of features in heavy quark measurements requires experimental measurement of B and D 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 vertex detector upgrade! • See Talk by Andrew Rose (1.4) Poor (wo)man’s approach to measure B/D contributions to non-photonic electrons---- e-h correlations X.Y. Lin, hep-ph/0602067 Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  6. PYTHIA Simulation of e-h Correlations • Associated pT > 0.3 GeV/c. • Significant difference in the near-side correlations. • Width of near-side correlations largely due to decay kinematics. B D X.Y. Lin, hep-ph/0602067 Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  7. Major Detectors Used Signal: Non-photonic electron Background: Hadron Photonic electron Charm decay Bottom decay Photon conversion π0Dalitz decay ηDalitz decay kaon decay vector meson decays Data Sample: p+p collisions at sNN = 200 GeV in year 5 run. 2.37 million EMC HT1 triggered events with threshold 2.6 GeV; 1.68 million EMC HT2 triggered events with threshold 3.5 GeV. • Time Projection Chamber (TPC) • Electro-Magnetic Calorimeter (EMC) • Shower Maximum Detector (SMD) Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  8. Electron ID Using TPC and EMC Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  9. Electron ID Using TPC and EMC • The purity of electron sample is above 98% up to pT ~ 6.5 GeV/c. Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  10. Photonic Background m<100 MeV/c2 • Electron candidates are combined with tracks passing a loose cut on dE/dx around the electron band. • The invariant mass for a pair of photonic electrons is small. • The combinatorial background is small in p+p collisions. • Reconstructed photonic = Opposite sign – Same sign. • Photonic electron = reconstructed-photonic/ ε. ε is the background reconstruction efficiency calculated from simulations. Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  11. Procedure to Extract the Signal of e-h Correlations Semi-inclusive electron • Signal: • non-photonic = semi-inclusive +combinatorics-(1/eff-1)*reco-photonic • Each item has its own corresponding Δφ histogram. Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  12. e-h Azimuthal Correlations after Bkgd. Subtraction Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  13. Use PYTHIA Curves to Fit Data Points B D • Fit function: R*PYTHIA_B+(1-R)*PYTHIA_D • R is B contribution, i.e. B/(B+D), as a parameter in fit function. Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  14. Use PYTHIA Curves to Fit Data Points • B/(B+D) consistent varying fit range. Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  15. Preliminary Results: B Contribution .VS. pT • Error bars are statistical only! • Data uncertainty includes statistic errors and systematic uncertainties from: ---- photonic background reconstruction efficiency (dominant). ---- difference introduced by different fit functions. • Preliminary data is within the range that FONLL calculation predicts. • Non-zero B contribution is observed. Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  16. Summary • Non-photonic electron and charged hadron correlations are sensitive to D and B contributions to non-photonic electrons. • We have measured e-h correlations in 200 GeV p+p collisions. • The preliminary data indicates at pT ~ 4-6 GeV/c the measured B contribution to non-photonic electrons is comparable to D contribution based on PYTHIA model. • Our measurement of B/(B+D) provides a constraint to the FONLL prediction. Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  17. Backup slides Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  18. Method to Extract the Signal of e-h Correlations non-pho. e= semi-incl. e +combinatorics - not-reco-pho. = semi-incl. e +combinatorics - (1/eff-1)*reco-pho. Δφnon-pho = Δφsemi-inc + Δφcombinatorics - Δφnot-reco-pho = Δφsemi-inc + Δφcombinatorics - (1/eff -1) *Δφreco-pho-no-partner • Note Δφnot-reco-pho = (1/eff -1) *Δφreco-pho-no-partner! Δφreco-pho-no-partneris the reco-pho after removing the conversion partner. • The photonic background has two parts: reco-pho and not-reco-pho. In electron yield or v2 analysis, the not-reco-pho part can just be calculated by reco-photonic part after an efficiency correction, i.e. not-reco-photonic = (1/eff-1)*reco-pho. • However, in e-h correlation analysis, that is different. The reco-pho electron means we find the conversion partner, while the not-reco-pho electron means we miss the conversion partner. The resulting e-h correlations for these two parts are different. If we use reco-pho part to calculate the not-reco-pho part, we have to remove the conversion partner of reco-pho part. Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  19. The distributions of ChiSquare .VS. ratio_B Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  20. The distributions of ChiSquare .VS. ratio_B Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  21. Preliminary Results: B Contribution .VS. pT Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  22. Electron Identification: Projection Distance -3σ < z distance < 3σ and -3σ < φdistance < 3σ were set to remove lots of random associations between TPC tracks and BEMC points. Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  23. PYTHIA Simulation: e pT .VS. parent pT • C-quark needs to have larger momentum than b-quark to boost the decayed electron to high pT. Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  24. PYTHIA Simulation: e pT .VS. hadron pT • The efficiency of associated pT cut is different between D decay and B decay. Therefore, it is better to use lower pT cut on the associated particles in order to avoid analysis bias! Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  25. PYTHIA Simulation: e pT .VS. hadron pT Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  26. PYTHIA parameters used in this analysis PYTHIA version: v6.22 δ fragmentation function used for both charm and bottom. Parameters for charm: PARP(67) = 4 (factor multiplied to Q2) <kt> = 1.5 GeV/c mc = 1.25 GeV/c2 Kfactor = 3.5 MSTP(33) =1 (inclusion of K factor) MSTP(32) = 4 (Q2 scale) CTEQ5L PDF Parameters for bottom are the same as for charm except mb = 4.8 GeV/c2. X.Y. Lin, hep-ph/0602067 Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  27. Near-side width due to decay kinematics All hadrons Hadrons from D Background with δ fragmentation function Quark Matter 2006, Shanghai, Nov. 14-20, 2006

  28. Near-side width does not strongly depend on FF 2.5-3.5 GeV/c 3.5-4.5 GeV/c 5.5-6.5 GeV/c 4.5-5.5 GeV/c • Will be included in the systematic uncertainties in the future. Quark Matter 2006, Shanghai, Nov. 14-20, 2006

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