1. Study of b quark contributions to non-photonic electron yields by azimuthal angular correlations between non-photonic electrons and hadrons Shingo Sakai for STAR collaboration Univ. of California, Los Angeles 1

2. Outline b/c separation in non-photonic electron at 200 GeV pp by electron-hadron (e-h & e-D 0 ) azimuthal correlation @ STAR Discuss heavy flavor energy loss in the dense matter 2

3. Parton energy loss  Gluon radiation model well represents R AA for neutral pion  The model predicts that heavier quarks lose smaller energy due to “dead cone” effect  The model predicts significant difference between bottom quark energy loss and light & charm quark energy loss. 3 Phys. Lett. B 632, 81 (2006)

4. Heavy flavor energy loss Phys. Rev. Lett. 98 (2007) 192301  Heavy flavor production has been studied by measuring electrons decay from charm and bottom (non-photonic electron) at RHIC  R AA for non-photonic electron is strong & consistent with hadrons  Indicate a large energy loss for heavy quarks in the dense matter.  Uncertainty from bottom quark contribution not only theory but also experiment 4

5. pQCD prediction for Bottom  Since charm and bottom are heavy, their production have been predicted by pQCD  FONLL predicts bottom quark contribution significant (c/b = 1) around 5 GeV/c in non-photonic electron yield with large uncertainty.  It’s important to experimentally determine bottom quark contribution to understand heavy flavor energy loss. *Uncertainty comes from mass, PDF, etc in the calculation *FONLL =A Fixed-Order plus Next- to-Leading-log 5

6. charm/bottom separation(1)  Monte Carlo simulation (PYTHIA) for e D -h and e B -h  Near side width for B decay is wider than that of D decay due to decay kinematics  measuring e-h correlation in pp & fit by MC with B/(B+D) as parameter e D - h e B - h 6

7. Charm/bottom separation (2)  e-D0 correlation  Request like-sign e-K pair o near-side ; bottom dominant o away-side ; charm dominant 7

8. STAR Experiment  Large acceptance Full azimuthal coverage => good for azimuthal correlation study  TPC measure momentum measure dE/dx  EMC + SMD measure energy measure shower shape => electron identification  TOF measure Time of flight => particles (π, K, p) identification 8

9. Particle Identification   /K separation to 1.6 GeV/c –0.7 for TPC Alone  (  +K)/p to p = 3 GeV/c –1.2 for TPC Alone electron Electron purity 98% for p T < 6 GeV/c 80% for 9 GeV/c @ pp 9 TOF

10. Photonic electron identification  Photonic electron is main background  Photonic electrons are experimentally reconstructed by calculating invariant mass at DCA for two electrons  request mass < 0.1  # of reconstructed photonic e  reconstruction efficiency ( ε reco ) is ~ 70% 10 a m (GeV/c 2 )

11. each distributions are experimentally determined. combinatorial 11  electron sample after removing opposite sign electron (inv. mass<0.1) forms “semi” inclusive electron.  Non-photonic electron can be calculated as; Method of Method of e HF - hadron correlation

12. e HF and hadron correlation  Azimuthal correlation between e HF and hadron  Experimental result is fit by simulation results e D – h (MC) e B – h (MC) fitting pp@200 GeV parameter for the fitting 12

13. e HF and D 0 correlation  making Kπ invariant mass for Δφ bins w.r.t trigger electron (S/B ~ 14% and significance ~ 3.7)  request same sign Kaon as triggered electron  Near side ; B dominant  Away side ; D dominant  compared with MC simulations to get B/D ratio 13 pp@200 GeV

14. B decay contribution  B decay contribution to non-photonic electron  B decay contribution increase with pT  B/D = 1.0 above 5 GeV/c  good agreement with pQCD (FONLL) prediction 14

15. Large Bottom energy loss ?  Bottom quark contribution is ~50% above 5 GeV/c @ pp => there would be bottom contribution in AuAu, too  R AA for non-photonic electron consistent with hadrons  Indicate large energy loss not only charm quark but also bottom quark. 15 C:B ~ 1:1 @ pp

16. R AA c & R AA b correlation (1)  R AA C and R AA B are connected B decay contribution @ pp  With the measurements of r @ pp and R AA, we can derive a relationship between R AA c and R AA b. 16

17. R AA c & R AA b correlation (2) o R AA c & R AA b correlation together with models o Dominant uncertainty is normalization in R AA analysis o R AA b < 1 ; B meson suppressed o prefer Dissociate and resonance model (large b energy loss) 17 I; Phys. Lett. B 632, 81 (2006) ; dN g /dy = 1000 II; Phys. Lett. B 694, 139 (2007) III; Phys.Rev.Lett.100(2008)192301 STAR preliminary p T >5 GeV/c

18. Summary Azimuthal correlation between non-photonic electron and hadron (e-h & e-D 0 ) has been measured at 200 GeV pp collisions @ RHIC-STAR The azimuthal angular correlation differs for non-photonic electrons from D and B semi-leptonic decays We compare our measured azimuthal correlation with those from D and B semi-leptonic decays from PYTHIA p+p simulations to derive the relative ratio of B/(B+D) Our result indicates comparable B and D contributions to non-photonic electrons for p T 2.5-9 GeV/c and it is consistent with FONLL calculation. Our measured B/D ratio would imply considerable b quark energy loss in medium based on R AA measurement from central Au+Au collisions 18