STAR Open Heavy Flavor Measurements

1. STAR Open Heavy Flavor Measurements Gang Wang (UCLA) • Motivation • D0 / Ds / D* • Non-photonic electron • Summary 1

2. X. Zhu, et al, Phys. Lett. B647, 366(2007). Why heavy quarks? - Higgs mass: electro-weak symmetry breaking (current quark mass). - QCD mass: Chiral symmetry breaking (constituent quark mass). • Strong interactions do not affect heavy-quark mass. • Initial fusion dominates heavy flavor production. • Study properties of the hot and dense medium at the early stage of heavy-ion collisions. • Light flavor thermalization. M. Gyulassy & Z. Lin, PRC 51 (1995) 2177 Charm quark

3. Large acceptance |h| < 1, 0 < f < 2p • TPC dE/dx, momentum • TOF 1/b difference The STAR detector and Particle ID p K p Run9 ~ 72% of full TOF Run10: 100% significantly improved PID for final state hadrons, especially for kaons 3

4. D0 PRL. 94 (2005) 62301 run3 Previous D0 measurements run4 STAR Preliminary ArXiv: 0805.0364

5. run4 run3 NPE+μ NPE+D0 NPE+μ+D0 STAR Preliminary ArXiv: 0805.0364 Nbin scaling • Charm x-section ~ Nbin. Difficulties: • Short life time • Low production rate • Large combinatorial bg

6. D0 in 200GeV p+p 0.4 < pT < 2.2 GeV/c Same sign Mixing event Track rotation run9 Yifei Zhang, DNP2010 talk Mass window: 1.72 – 2.1 GeV/c2 ~ 4s signal observed.

7. Dsin 200GeV Au+Au with the help of Silicon Vertex Tracker. • Assume pT spectrum shape similar to D0: 47% yield covered. • D± yields estimated from D±/D0 ratio from e+e- data. run7 I.Kuznetsova, J. Rafelski, Eur. Phys. J. C 51 1 (2007) 113-133 Sarah LaPointe, WWND2010 talk Preliminary results indicate statistical hadronization.

8. D*in 200GeV p+p run4 Background combinations: Wrong sign: D0 and -, D0bar and + Side band: 1.72< M(K) < 1.80 or 1.92 < M(K) < 2.0 GeV/c2 Yifei Zhang, DNP2010 talk All triggers included. More than 4s signal at low pT and very significant at high pT - mostly from EMC-based high neutral energy triggers.

9. No significant charge asymmetry D*in 200GeV p+p STAR Preliminary All triggers included. More than 4s signal at low pT and very significant at high pT - mostly from EMC-based high neutral energy triggers. Wrong sign and side-band method reproduce background well. Yifei Zhang, DNP2010 talk 9

10. Summary: D mesons • Previous STAR NPE/μ/D0 measurents in Au+Au and d+Au show the Nbin scaling of charm x-section. • STAR Dsmeasurement in Au+Au tends to support the statistical hadronization model. • Open charm hadrons are reconstructed from STAR run9 p+p 200 GeV data. • 4 sD0 signal at low pT and more significant D* signal at high pT are observed. • Working on efficiency for pT spectra and cross-section. 10

11. Photon conversions p0 → g g, g→ e+ e- in material Dalitz decays p0 → ge+ e- Heavy flavor electrons D/B → e± + X Weak Kaon decays Ke3: K± → p0e±e < 3% contribution in pT > 1 GeV/c Vector Meson Decays w, , fJ,  → e+e- < 15% contribution in all pT Electron signal and background Non-photonic electron Photonic electron 11

12. Long and slowly dying issue on RHIC NPE STAR STAR PRL 97(2007)192301 PHENIX PRL 98(2007)172301 run3 STAR d+Au PRL 94(2005)62301 PRL 97(2006)252002 PRL 94(2005)082301 • Results differ by a factor of two in • pT spectra • Total cross section • p+p collisions • Au+Au collisions • Investigation is underway 12

13. STAR efforts STAR preliminary Beam pipe + SVT + SSD+ Dalitz • Significantly Increase the S/B of this analysis (2008-present) • Cross check NPE measurements with early runs. Count Beam pipe + Dalitz TPC Inner Field cage R(cm) Wei Xie, HP2010 talk 13 Yield of conversion electrons at different radial location

14. STAR high pT NPE in 200GeV p+p Wei Xie, HP2010 talk • Measurement done using TPC+EMC using run08 and run05 data. • pT>2.5GeV/c NPE measurement with dramatically different background agree with each other very well • Combined using “Best Linear Unbiased Estimate”. χ2/ndf = 4.81/7 = 0.69 14

15. Comparison with the Published NPE Results Wei Xie, HP2010 talk • STAR and PHENIX NPE result in 200GeV p+p collisions • consistent within errors at pT > 2.5 GeV/c • STAR High pT NPE results are consistent with FONLL in 200GeV p+p collisions 15 See Wenqin Xu's talk for details on eB x-section!

16. Near Side: what’s the contribution of B/D decay to the non-photonic electrons? trigger Motivations Conical Pattern in 2-Particle Correlations in Au+Au Collisions pTtrig= 3-4.0 GeV/c; pTasso = 0.5-1 GeV/c What if we trigger on non-photonic electrons? Away Side in medium: How does B/D lose energy? Via conical emission? 16

17. Study of heavy flavor via non-photonic electrons PYTHIA • Dmesons have their directions well represented by the daughter electrons, above 1.5 GeV/c. • Electrons from B decays can represent the B meson momentum direction well if pT > 3 GeV/c. 17

18. Disentangle Charm and Bottom Production B • Wider φ distribution for B meson because of the larger mass. • Combined fit on data to obtain the B meson contribution to non-photonic electron. D hep-ph/0602067

19. B Meson Suppression in 200 GeV Au+Au Phys. Rev. Lett. 105 (2010) 202301 run5&6 • ~30-60% of non-photonic electron come from B meson in 200GeV p+p collisions. • Assume the same fraction in Au+Au collisions, results indicate B meson is suppressed See Andre Mischke's talk for details! 19

20. NPE-h Correlation in 500 GeV p+p Wei Li (ATHIC2010 talk) run9 • Raw NPE-h correlation without pile-up removal in 500GeV p+p collisions. • PYTHIA simulation still shows different near-side peaks for NPE from D and B. 20

21. Broadened Awayside in the NPE-h Correlations CuCu AuAu 34.4 / 5 21.7 / 5 B. Biritz (QM2009) run5 run7 0 – 20%: 3 < pTtrig< 6 GeV/c & 0.15 < pTasso< 0.5 GeV/c Away side broadened, beyond PYHTIA fit, in both the Au+Au and the Cu+Cu collisions 21

22. Non-photonic e-h correlations in d+Au 200 GeV 3 < pTtrig< 6 GeV/c & 0.15 < pTasso< 0.5 GeV/c run8 The away-side correlation can be well described by PYTHIA calculations for p+p. No medium effects seen here. Gang Wang, HP2010 talk

23. Motivations Partonic flow picture is supported for u, d, s. What about heavier quarks? PHENIX, arXiv:nucl-ex/0604011; STAR, Nucl. Phys. A 830(2009)19c. Above 1.5 GeV/c, D-decay electrons well represent the mother D mesons’ direction. eDv2 ~ D v2 Similarly, above 3 GeV/c, eBv2 ~ B v2

24. NPEv2 run7 Non-photonic e v2 is lower than hadron v2 (or KS0, Λ). STAR, Phys. Rev. C 77 (2008) 54901 Gang Wang, HP2010 talk 24

25. Discrepancy in high pT NPE has been solved! • NPE-h correlations have been measured in p+p collisions to retrieve B and D contributions, and used to study B energy loss. • Using d+Au as a reference, the shape of NPE-h correlation on the away-side is found to be modified in central Cu+Cu and Au+Au collisions due to the presence of the dense medium created in these collisions. • NPE v2 values obtained via fitting the correlations fall in a reasonable range, and are lower than hadron(or KS0, Λ) v2. • Correlations with heavy flavor tag: jet reconstruction, ridge.. Summary: NPE 25

26. Future of Heavy Flavor Measurement at STAR MTD (MRPC) See Xin Dong's talk for details! 26

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28. Disentangle Charm and Bottom Production STAR preliminary JPG35(2008)104117 JPG35(2008)104117 • Near side: mostly from B mesons • Away side: charm (~75%), Bottom (~25%)

29. K*in 200GeV p+p K*0 0.4 < pT < 2.2 GeV/c K2*(1430) Yifei Zhang, DNP2010 talk Run 9 p+p 200 GeV 105M minbias events Three different methods to reproduce combinatorial background. Very good K*0 and K2*(1430) signal observed.

30. Energy loss mechanisms of non-photonic Electrons l l u u u l K+ K+ Hot/Dense Medium c quark e-/- c c light D0 D0 D0 meson energy loss Ivan, et al K+ Hot/Dense Medium “dead cone effect”: gluon radiation suppressed at q< mQ/EQ c quark e-/- c D0 radiative energy loss (D. kharzeev, M.Djordjevicet al. ) Hot/Dense Medium c quark e-/- collision energy loss (Teany, Ralf, Denes et al.) 30 Wei Xie, HP2010 talk