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Heavy Quark Measurements by Weak-Decayed Electrons at RHIC-PHENIX. Fukutaro Kajihara (CNS, University of Tokyo) for the PHENIX Collaboration. Introduction. Dir. g. p 0 h. Very large jet-quenching and elliptic flow (v2) have been observed for light quarks and gluons at RHIC
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Heavy Quark Measurements by Weak-Decayed Electrons at RHIC-PHENIX Fukutaro Kajihara (CNS, University of Tokyo) for the PHENIX Collaboration
Introduction Dir. g p0h • 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 ( gb < 4 ) at RHIC • HQ provides further insight into medium property at RHIC “Strongly interacting, high dense, and perfect fluid has been observed in RHIC”
Heavy Quark Measurement by Single Electrons Single electrons from semileptonic decays were first measured to extract charm at CERN-ISR in early 1970’s. F. W. Busser et al, PLB53, 212 Direct Measurement: DKp, DKpp Indirect Measurement via Semileptonic decays Branching ratio is relatively large p+
Electron Measurement in PHENIX Central Arm Detectors: |h|<0.35 Df = p (2 arms x p/2) Electron ID : RICH, EMC Tracking : DC, PC, EMC e- Centrality, Npart, Ncol : BBC, ZDC + Glauber model
Electron Signal and Background Photon conversions p0 → g g, g→ e+ e- in material Main background Dalitz decays p0 → ge+ e- Direct Photon Very small Measured by PHENIX Heavy flavor electrons D → e± + X Weak Kaon decays Ke3: K± → p0e±e < 3% of non-photonic in pT > 1.0 GeV/c Vector Meson Decays w, , fJ → e+e- < 2-3% of non-photonic in all pT Photonic electron Non-photonic electron Background is subtracted by two independent techniques
Run-5 p+p Result at s = 200 GeV PRL, 97, 252002 (2006) Heavy flavor electron compared to FONLL Data/FONLL = 1.71 ± 0.019 (stat.)± 0.18 (sys.) Total cross section of charm production: 567 mb ± 57 (stat.) ± 224 (sys.) All Run-2, 3, 5 p+p data are consistent within errors Upper limit of FONLL Provides crucial reference for heavy ion measurement
Run-4 Au+Au Result at sNN = 200 GeV PRL, 98, 172301 (2007) 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 In low pT, spectra in Au+Au agree with p+p reference MB Clear high pT suppression in central collisions The inside box shows signal to background ratio. S/B > 1 for pT > 2 GeV/c p+p
Nuclear Modification Factor: RAA Total error from p+p Suppression level is the almost same asp0 andhin high pT region Binary scaling works well for p’T>0.3 GeV/c integration (Total charm yield is not changed)
Elliptic Flow: v2 1 Kaon contribution is subtracted • Elliptic flow: dN/dφ ∝ N0(1+2 v2 cos(2φ)) Collective motion in the medium • v2 forms in the partonic phase before hadrons are made of light quarks (u/d/s) →partonic level v2 • If charm quarks flow, • - partonic levelthermalization • - high density at the early stage • of heavy ion collisions Non-zero elliptic flow for heavy-flavor electron → indicatesnon-zero D v2
RAA and v2 of Heavy Flavor Electrons PRL, 98, 172301 (2007) • Only radiative energy loss model can not explain RAA and v2 simultaneously. • Rapp and Van Hees • Phys.Rev.C71:034907,2005 • Simultaneously describes RAA and v2 with diffusion coefficient in range: DHQ × 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 DHQ. Comparable to QGP life time.
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 sNN = 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. Non-zero v2 of heavy flavor electrons has been observed. Only radiative energy loss model can not explain RAA and v2 simultaneously. • 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.
Consistency Check of Two Methods PRL, 97, 252002 (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 PRL, 97, 252002 (2006)
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)
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.
Background Subtraction: Converter Method 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 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)
