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

Introduction

Next challenge: light heavy quarks (HQ: charm and bottom)HQ has large massHQ has larger thermalization time than light quarksHQ is produced at the very early time by hard collisionsHQ 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 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

Heavy Quark Measurement by Single ElectronsIndirect Measurement via Semileptonic decaysp+Direct Measurement:DKp, DKppBranching ratio is relatively large

Electron Measurement in PHENIXe-Central Arm Detectors: |h|

Electron Signal and BackgroundPhoton conversions p0 g g, g e+ e- in materialMain backgroundDalitz decaysp0 g e+ e- Direct PhotonVery smallMeasured by PHENIXHeavy flavor electronsD e + XWeak Kaon decaysKe3: K p0 e e < 3% of non-photonic in pT > 1.0 GeV/cVector Meson Decaysw, , fJ e+e- < 2-3% of non-photonic in all pT

Photonic electronNon-photonic electronBackground is subtracted by two independent techniques

Results

Run-5 p+p Result at s = 200 GeVHeavy flavor electroncompared to FONLL

Data/FONLL = 1.71 0.019 (stat.) 0.18 (sys.)

Total cross section of charmproduction: 567 mb 57 (stat.) 224 (sys.)

All Run-2, 3, 5 p+p data areconsistent within errorsPRL, 97, 252002 (2006)Upper limit of FONLLProvides crucial reference for heavy ion measurement

Run-4 Au+Au Result at sNN = 200 GeVClear high pT suppression in central collisionsPRL, 98, 172301 (2007)MBp+pHeavy flavor electron in Au+Au compared to p+p reference

Solid lines: FONLL normalized to p+p data and scaled by number of binary collisionsThe inside box shows signal to background ratio.S/B > 1 for pT > 2 GeV/c In low pT, spectra in Au+Au agree with p+p reference

Nuclear Modification Factor: RAASuppression level is the almost same as p0 and h in high pT regionBinary scaling works well for pT>0.3 GeV/c integration (Total charm yield is not changed)

Elliptic Flow: v2 Non-zero elliptic flow for heavy-flavor electron indicates non-zero D v2 Elliptic flow: dN/d N0(1+2 v2 cos(2)) 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 level thermalization - high density at the early stage of heavy ion collisions

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 HeesPhys.Rev.C71:034907,2005 Simultaneously describes RAA and v2 with diffusion coefficient in range: DHQ 2T ~ 4 6

Assumption: elastic scattering is mediated by resonance of D and B mesons. They suggest that small thermalization time (~ a few fm/c) and/or DHQ.Comparable to QGP life time.

Summaryp+p collisions at s = 200 GeV in mid rapidity New measurement of heavy flavor electrons for 0.3 < 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.

OutlookD meson measurement in p+p by electron and Kp measurement. High statistic Cu+Cu analysis.Single m measurement in forward rapidity.D/B direct measurement by Silicon Vertex Tracker.

Thank you

Backup slides

Consistency Check of Two MethodsPRL, 97, 252002 (2006) PRL, 97, 252002 (2006)Both methods were always checked each otherEx. Run-5 p+p in leftLeft top figure shows Converter/Cocktail ratio of photonic electronsLeft bottom figure shows non-photon/photonic ratio

Motivations in Au+Au at sNN = 200 GeVG.D. Moore, D Teaney PR. C71, 064904 (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 fluidityHQ RAA and v2 (in Shingos talk) can be used to determine D

Most sources of backgroundhave 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

Background Subtraction: Converter MethodWe know precise radiation length (X0) of each detector materialThe photonic electron yield can be measured by increase of additional material (photon converter was installed)Advantage is small systematic error in low pT regionBackground in non-photonic issubtracted by cocktail method

Photon Converter (Brass: 1.7% X0)