Heavy Quark Measurement by Single Electrons in the PHENIX Experiment

1. Heavy Quark Measurement by Single Electrons in the PHENIX Experiment Fukutaro Kajihara (CNS, University of Tokyo) for the PHENIX Collaboration

2. Dir. g p0h Introduction • Very large suppression and v2 have been observed for light quarks and gluons at RHIC • Parton energy loss and hydrodynamics explain them successfully • Next challenge: light heavy quark (HQ: charm and bottom) • HQ has large mass • HQ has larger thermalization time than light quarks • HQ is produced at the very early time • HQ is not ultra-relativistic ( gv < 4 ) • HQ will help systematic understanding of medium property at RHIC • Experimental approach: Electrons from semi-leptonic heavy flavor decays in mid rapidity (||<0.35)

3. Motivations in p+p at s = 200 GeV • HQ Production Mechanism • Due to large mass, HQ productions are considered as point-like pQCD processes • HQ is produced at the initial via leading gluon fusion, and sensitive to the gluon PDF • FONLL pQCD calculation describes our single electron results in Run-2 and Run-3 within theoretical uncertainties • Important References • RAA calculation of HQ • Important input for J/y studies

4. Motivations in Au+Au at sNN = 200 GeV Energy loss and flow are related to the transport properties of the medium in HIC: Diffusion constant (D) Moreover, D is related to viscosity/entropy density ratio (/s) which ratio could be very useful to know the perfect fluidity HQ RAA and v2 (in Shingo’s talk) can be used to determine D G.D. Moore, D Teaney PR. C71, 064904 (2005)

5. Data Analysis

6. Electron Signal and Background [Photonic electron] … Background • Conversion of photons in material Main photon source: p0 → gg In material: g → e+e- (Major contribution of photonic electron) • Dalitz decay of light neutral mesons p0 → g e+e- (Large contribution of photonic) • The other Dalitz decays are small contributions • Direct Photon (is estimated as very small contribution) • Heavy flavor electrons (the most of all non-photonic) • Weak Kaon decays Ke3: K± → p0 e±e (< 3% of non-photonic in pT > 1.0 GeV/c) • Vector Meson Decays w, , fJ → e+e-(< 2-3% of non-photonic in all pT.) [Non-photonic electron] … Signal and minor background

7. Background Subtraction: Cocktail Method Most sources of background have been measured in PHENIX Decay kinematics and photon conversions can be reconstructed by detector simulation Then, subtract “cocktail” of all background electrons from the inclusive spectrum Advantage is small statistical error.

8. Ne Electron yield converter 0.8% 0.4% 1.7% With converter Photonic W/O converter Dalitz : 0.8% X0 equivalent radiation length Non-photonic 0 Material amounts: 0 Background Subtraction: Converter Method We know precise radiation length (X0) of each detector material The photonic electron yield can be measured by increase of additional material (photon converter was installed) Advantage is small systematic error in low pT region Background in non-photonic is subtracted by cocktail method Photon Converter (Brass: 1.7% X0)

9. Consistency Check of Two Methods Accepted by PRL (hep-ex/0609010) Both methods were always checked each other Ex. Run-5 p+p in left Left top figure shows Converter/Cocktail ratio of photonic electrons Left bottom figure shows non-photon/photonic ratio Accepted by PRL (hep-ex/0609010)

10. New Results are Available!! • Run-5 p+p result at s = 200 GeV • Run-4 Au+Au result at sNN = 200 GeV • Improvements over QM05: • Higher statistics and smaller systematic error • pT range is extended: 0.3<pT<9.0 GeV/c • Both cocktail and converter methods • Nonphotonic/Photonic ratio updates v2 calculation (in Shingo’s talk)

11. Run-5 p+p Result at s = 200 GeV Accepted by PRL (hep-ex/0609010) Heavy flavor electron compared to FONLL Data/FONLL = 1.71 +/- 0.019 (stat)+/- 0.18 (sys) FONLL agrees with data within errors All Run-2, 3, 5 p+p data are consistent within errors Total cross section of charm production: 567 mb +/- 57 (stat) +/- 224 (sys) Upper limit of FONLL

12. Run-4 Au+Au Result at sNN = 200 GeV Submitted to PRL (nucl-ex/0611018) Heavy flavor electron compared to binary scaled p+p data (FONLL*1.71) Clear high pT suppression in central collisions S/B > 1 for pT > 2 GeV/c (according to inside figure) MB p+p

13. Nuclear Modification Factor: RAA p+p reference: Data (converter) for pT<1.6 [GeV/c] 1.71*FONLL for pT>1.6 [GeV/c] Suppression level is the almost same as p0 and h in high pT region

14. Integrated RAA vs. Npart Binary scaling works well for pT>0.3 GeV/c integration (about 50% of total charm yield) Clear suppression is seen for pT>3.0 GeV/c integration Suppression of D meson is probably less than p0 Submitted to PRL (nucl-ex/0611018) Total error from p+p

15. (I) pQCD calculation with radiative energy loss • Large parton densities and strong coupling ( ~ 14 GeV2/fm) • Light hadron suppression is also described with the same value Comparisons with Theories • (II) (III) include elastic collision mechanism of HQ • Their models provide diffusion constant D (2pT*D=4-6 in (II)) Submitted to PRL (nucl-ex/0611018) See combined RAA and v2 discussion in Shingo’s talk Anyway, charm/bottom identification is needed for more development 0-10 % centrality

16. Summary • p+p collisions at s=200 GeV in mid rapidity New measurement of heavy flavor electrons for0.3 < pT < 9.0 GeV/c FONLL describes the measured spectrum within systematic error (Data/FONLL = 1.7) • Au+Au collisions at s=200 GeV in mid rapidity Heavy flavor electrons are measured for 0.3 < pT < 9.0 GeV/c Binary scaling of integrated charm yield (pT > 0.3 GeV/c) works well RAA shows a strong suppression for high pT region • Outlook D meson measurement in p+p by electron and Kp measurement High statistic Cu+Cu analysis Single m measurementin forward rapidity D/B direct measurement by Silicon Vertex Tracker

17. 13 Countries; 62 Institutions; 550 Participants*

18. Backup slides