1 STAR Open Heavy Flavor Measurements Gang Wang (UCLA) 1  Motivation  D 0 / D s / D*  Non-photonic electron  Summary

2 Why heavy quarks? X. Zhu, et al, Phys. Lett. B647, 366(2007). - 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

The STAR detector and Particle ID Large acceptance |  | < 1, 0 <  < 2   p   TPC dE/dx, momentum  TOF 1/  difference Run9 ~ 72% of full TOF Run10: 100% significantly improved PID for final state hadrons, especially for kaons 3

4 Previous D 0 measurements STAR Preliminary ArXiv: run4 D0D0 PRL. 94 (2005) run3

5 N bin scaling  Charm x-section ~ Nbin. STAR Preliminary ArXiv: run4 run3 NPE+D 0 NPE+μ+D 0 NPE+μ Difficulties:  Short life time  Low production rate  Large combinatorial bg

D 0 in 200GeV p+p Mass window: 1.72 – 2.1 GeV/c 2 ~ 4  signal observed. Yifei Zhang, DNP2010 talk 0.4 < p T < 2.2 GeV/c Mixing event Track rotation Same sign run9

7 D s in 200GeV Au+Au Preliminary results indicate statistical hadronization. Assume p T spectrum shape similar to D 0 : 47% yield covered. D ± yields estimated from D ± /D 0 ratio from e+e- data. with the help of Silicon Vertex Tracker. Sarah LaPointe, WWND2010 talk I.Kuznetsova, J. Rafelski, Eur. Phys. J. C 51 1 (2007) run7

8 D* in 200GeV p+p Background combinations: Wrong sign: D 0 and  -, D 0 bar and  + Side band: 1.72< M(K  ) < 1.80 or 1.92 < M(K  ) < 2.0 GeV/c 2 All triggers included. More than 4  signal at low p T and very significant at high p T - mostly from EMC-based high neutral energy triggers. Yifei Zhang, DNP2010 talk run4

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

Summary: D mesons  Previous STAR NPE/μ/D 0 measurents in Au+Au and d+Au show the N bin scaling of charm x-section.  STAR D s measurement in Au+Au tends to support the statistical hadronization model.  Open charm hadrons are reconstructed from STAR run9 p+p 200 GeV data.  4  D 0 signal at low p T and more significant D* signal at high p T are observed.  Working on efficiency for p T spectra and cross- section. 10

Photon conversions    →   → e + e - in material  Dalitz decays    →  e + e - Heavy flavor electrons D/B → e ± + X  Weak Kaon decays K e3 : K ± →   e ± e 1 GeV/c  Vector Meson Decays  J  → e + e - < 15% contribution in all p T Photonic electron Non-photonic electron Electron signal and background 11

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

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

14 STAR high p T NPE in 200GeV p+p Measurement done using TPC+EMC using run08 and run05 data. p T >2.5GeV/c NPE measurement with dramatically different background agree with each other very well Combined using “ Best Linear Unbiased Estimate”. χ 2 /ndf = 4.81/7 = Wei Xie, HP2010 talk

15 Comparison with the Published NPE Results STAR and PHENIX NPE result in 200GeV p+p collisions consistent within errors at p T > 2.5 GeV/c STAR High p T NPE results are consistent with FONLL in 200GeV p+p collisions 15 Wei Xie, HP2010 talk See Wenqin Xu's talk for details on e B x-section!

Away Side in medium : How does B/D lose energy? Via conical emission? Conical Pattern in Conical Pattern in 2-Particle Correlations in Au+Au Collisions p T trig = GeV/c; p T asso = GeV/c Motivations Near Side: what ’ s the contribution of B/D decay to the non- photonic electrons? trigger What if we trigger on non-photonic electrons? 16

Study of heavy flavor via non-photonic electrons D mesons 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 p T > 3 GeV/c. PYTHIA 17

18 Disentangle Charm and Bottom Production 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. B D hep-ph/

19  ~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 19 B Meson Suppression in 200 GeV Au+Au See Andre Mischke's talk for details! Phys. Rev. Lett. 105 (2010) run5&6

20  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 NPE-h Correlation in 500 GeV p+p Wei Li (ATHIC2010 talk) run9

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

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

23 Above 1.5 GeV/c, D-decay electrons well represent the mother D mesons ’ direction. e D v 2 ~ D v 2 Similarly, above 3 GeV/c, e B v 2 ~ B v 2 Partonic flow picture is supported for u, d, s. What about heavier quarks? Motivations PHENIX, arXiv:nucl-ex/ ; STAR, Nucl. Phys. A 830(2009)19c.

NPE v 2 Non-photonic e v 2 is lower than hadron v 2 (or K S 0, Λ). STAR, Phys. Rev. C 77 (2008) Gang Wang, HP2010 talk 24 run7

Summary: NPE  Discrepancy in high p T 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 v 2 values obtained via fitting the correlations fall in a reasonable range, and are lower than hadron(or K S 0, Λ) v 2.  Correlations with heavy flavor tag: jet reconstruction, ridge.. 25

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

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

K* in 200GeV p+p Three different methods to reproduce combinatorial background. Very good K* 0 and K 2 *(1430) signal observed. K* 0 K 2 *(1430) Run 9 p+p 200 GeV 105M minbias events Yifei Zhang, DNP2010 talk 0.4 < p T < 2.2 GeV/c

30 Energy loss mechanisms of non-photonic Electrons D0D0 radiative energy loss c quark K+K+ l e-/-e-/- light (D. kharzeev, M.Djordjevic et al. ) u c “dead cone effect”: gluon radiation suppressed at  < m Q /E Q collision energy loss c quark Hot/Dense Medium (Teany, Ralf, Denes et al.) D0D0 K+K+ l e-/-e-/- D0D0 meson energy loss c quark u c Hot/Dense Medium Ivan, et al u c D0D0 K+K+ l e-/-e-/- 30 Wei Xie, HP2010 talk