Fukutaro Kajihara (CNS, University of Tokyo) for the PHENIX Collaboration Heavy Quark Measurements by Weak-Decayed Electrons at RHIC-PHENIX

2 Introduction “Strongly interacting, high dense, and perfect fluid has been observed in RHIC”  0  Dir.  Very large jet-quenching and elliptic flow (v2) have been observed for light quarks and gluons at RHIC Parton energy loss in high dense medium and hydro- dynamics explain them successfully Next challenge: light → heavy quarks (HQ: charm and bottom) –HQ has “large mass” –HQ has larger thermalization time than light quarks –HQ is produced at the very early time by hard collisions –HQ is not ultra-relativistic (  < 4 ) at RHIC HQ provides further insight into medium property at RHIC

3 Indirect Measurement via Semileptonic decays ++ Heavy Quark Measurement by Single Electrons Direct Measurement: D  K , D  K  MesonD ±,D 0 Mass1869 (1865) MeV BR: D 0 → K  (3.85 ± 0.10) % BR: D → e +XD ± : 17.2, D 0 : 6.7 % Branching ratio is relatively large F. W. Busser et al, PLB53, 212 Single electrons from semileptonic decays were first measured to extract charm at CERN-ISR in early 1970’s.

4 Electron Measurement in PHENIX e-e- Central Arm Detectors:  0.35  (2 arms x  /2) Centrality, N part, N col : BBC, ZDC + Glauber model Electron ID : RICH, EMC Tracking : DC, PC, EMC

5 Electron Signal and Background Photon conversions    →   → e + e - in material Main background Dalitz decays    →  e + e - Direct Photon Very small Measured by PHENIX Heavy flavor electrons D → e ± + X 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 Non-photonic electron Background is subtracted by two independent techniques

6 Results

7 Run-5 p+p Result at  s = 200 GeV Heavy flavor electron compared to FONLL Data/FONLL = 1.71 ± (stat.) ± 0.18 (sys.) Total cross section of charm production: 567  b ± 57 (stat.) ± 224 (sys.) All Run-2, 3, 5 p+p data are consistent within errors PRL, 97, (2006) Upper limit of FONLL Provides crucial reference for heavy ion measurement

8 Run-4 Au+Au Result at  s NN = 200 GeV Clear high p T suppression in central collisions PRL, 98, (2007) MB p+p Heavy flavor electron in Au+Au compared to p+p reference Solid lines: FONLL normalized to p+p data and scaled by number of binary collisions The inside box shows signal to background ratio. S/B > 1 for pT > 2 GeV/c In low p T, spectra in Au+Au agree with p+p reference

9 Nuclear Modification Factor: R AA Suppression level is the almost same as  0 and  in high p T region Total error from p+p Binary scaling works well for p’ T >0.3 GeV/c integration (Total charm yield is not changed)

10 Elliptic Flow: v 2 1 Non-zero elliptic flow for heavy-flavor electron → indicates non-zero D v 2 Kaon contribution is subtracted Elliptic flow: dN/dφ ∝ N 0 (1+2 v 2 cos(2φ)) Collective motion in the medium v 2 forms in the partonic phase before hadrons are made of light quarks (u/d/s) → partonic level v 2 If charm quarks flow, - partonic level thermalization - high density at the early stage of heavy ion collisions

11 R AA and v 2 of Heavy Flavor Electrons PRL, 98, (2007) Only radiative energy loss model can not explain R AA and v 2 simultaneously. Rapp and Van Hees Phys.Rev.C71:034907,2005 Simultaneously describes R AA and v 2 with diffusion coefficient in range: D HQ × 2πT ~ 4 – 6 Assumption: elastic scattering is mediated by resonance of D and B mesons. They suggest that small thermalization time τ(~ a few fm/c) and/or D HQ. Comparable to QGP life time.

12 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 NN = 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. Non-zero v 2 of heavy flavor electrons has been observed. Only radiative energy loss model can not explain R AA and v 2 simultaneously. 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.

13 Thank you

14 Backup slides

15 Consistency Check of Two Methods PRL, 97, (2006) 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

16 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

17 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

18 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