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

2  0  Dir.  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 (  v < 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 R AA calculation of HQ Important input for J/  studies

4 Motivations in Au+Au at  s NN = 200 GeV G.D. Moore, D Teaney PR. C71, (2005) 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 R AA and v2 (in Shingo ’ s talk) can be used to determine D

5 Data Analysis

6 Electron Signal and Background Conversion of photons in material Main photon source:    →  In material:  → e + e - (Major contribution of photonic electron) Dalitz decay of light neutral mesons    →  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 K e3 : K ± →   e ± e ( 1.0 GeV/c) Vector Meson Decays  J  → e + e -  (< 2-3% of non-photonic in all p T. ) [Photonic electron] … Background [Non-photonic electron] … Signal and minor background

7 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. Background Subtraction: Cocktail Method

8 Background Subtraction: Converter Method We know precise radiation length (X 0 ) 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 p T region Background in non-photonic is subtracted by cocktail method Photon Converter (Brass: 1.7% X 0 ) N e Electron yield Material amounts:  0 0.4%1.7% Dalitz : 0.8% X 0 equivalent radiation length 0 With converter W/O converter 0.8% Non-photonic Photonic converter

9 Consistency Check of Two Methods Accepted by PRL (hep-ex/ ) 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

10 New Results are Available!! Run-5 p+p result at  s = 200 GeV Run-4 Au+Au result at  s NN = 200 GeV Improvements over QM05: Higher statistics and smaller systematic error p T range is extended: 0.3<p T <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 Heavy flavor electron compared to FONLL Data/FONLL = / (stat) +/ (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  b +/- 57 (stat) +/- 224 (sys) Accepted by PRL (hep-ex/ ) Upper limit of FONLL

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

13 Nuclear Modification Factor: R AA p+p reference: Data (converter) for p T <1.6 [GeV/c] 1.71*FONLL for p T >1.6 [GeV/c] Suppression level is the almost same as  0 and  in high pT region

14 Integrated R AA vs. N part Binary scaling works well for p T >0.3 GeV/c integration (about 50% of total charm yield) Clear suppression is seen for p T >3.0 GeV/c integration Suppression of D meson is probably less than  0 Submitted to PRL (nucl-ex/ ) Total error from p+p

15 Comparisons with Theories Submitted to PRL (nucl-ex/ ) (I) pQCD calculation with radiative energy loss Large parton densities and strong coupling ( ~ 14 GeV 2 /fm) Light hadron suppression is also described with the same value Anyway, charm/bottom identification is needed for more development See combined R AA and v2 discussion in Shingo ’ s talk 0-10 % centrality (II) (III) include elastic collision mechanism of HQ Their models provide diffusion constant D (2  T*D=4-6 in (II))

16 Summary p+p collisions at  s=200 GeV in mid rapidity New measurement of heavy flavor electrons for 0.3 < p T < 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 < p T < 9.0 GeV/c Binary scaling of integrated charm yield (p T > 0.3 GeV/c) works well R AA shows a strong suppression for high p T region Outlook D meson measurement in p+p by electron and K  measurement High statistic Cu+Cu analysis Single  measurement in forward rapidity D/B direct measurement by Silicon Vertex Tracker

17 13 Countries; 62 Institutions; 550 Participants*

18 Backup slides