Shingo Sakai for STAR collaboration Univ. of California, Los Angeles

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

2. Outline • b/c separation in non-photonic electron at 200 GeV pp by electron-hadron (e-h & e-D0) azimuthal correlation @ STAR • Discuss heavy flavor energy loss in the dense matter

3. Parton energy loss • Gluon radiation model well • represents RAA 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. Phys. Lett. B 632, 81 (2006)

4. Heavy flavor energy loss • Heavy flavor production has been • studied by measuring electrons • decay from charm and bottom • (non-photonic electron) • at RHIC • RAA 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 Phys. Rev. Lett. 98 (2007) 192301

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

6. charm/bottom separation(1) eD - h eB - h • Monte Carlo simulation (PYTHIA) for eD-h and eB-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

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

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

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

10. Photonic electron identification • Photonic electron (γ conversion, Dalitz) 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 (εreco) • is ~ 70% a m (GeV/c2)

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

12. eHF and hadron correlation pp@200 GeV eD – h (MC) eB – h (MC) fitting • Azimuthal correlation between eHF and hadron • Experimental result is fit by simulation results parameter for the fitting

13. eHF and D0 correlation pp@200 GeV • 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

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

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

16. RAAc & RAAb correlation (1) • RAAC and RAAB are connected B decay contribution @ pp • With the measurements of r @ pp and RAA, • we can derive a relationship between RAAc and RAAb.

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

18. Summary • Azimuthal correlation between non-photonic electron and hadron (e-h & e-D0) 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 pT 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 RAA measurement from central Au+Au collisions