Elliptic flow of electrons/positrons in 200 GeV Au+Au collisions at RHIC-PHENIX 坂井　真吾　for the PHENIX Collaboration Shingo Sakai 　 Univ. of Tsukuba for the PHENIX Collaboration

Motivation(1) Clear excess about 1 GeV/c with respect Page 1 g conversion p0  gee h  gee, 3p0 w  ee, p0ee f  ee, hee r  ee h’  gee From Run1 result (PHENIX: PRL 88(2002)192303) Electron source Dalitz decays Di-electron decays Photon conversions Kaon decays Thermal dileptons charm decay beauty decay Inc.e/pho.e Electron sorce From Rnn1 resul Consiten Photonic Above 1 GeV/c charm decay contribution is large high pt electron v2 can carry information about the anisotropy of the parent charmed mesons PYTHIA Inc.e/pho.e High pt energy loss ? Clear excess about 1 GeV/c with respect to photon conversion and light hadron decay.

Motivation(2) The photonic-subtracted electron Page 2 direct g (J. Alam et al. PRC 63(2001)021901) b c The photonic-subtracted electron single spectra consistent with charm decay (binary scaled). “The high pt electron v2 can carry information about the anisotropy of the parent charmed mesons. “ PYTHIA Electron sorce From Rnn1 resul Consiten Photonic Above 1 GeV/c charm decay contribution is large high pt electron v2 can carry information about the anisotropy of the parent charmed mesons PYTHIA High pt energy loss ? photonic-subtracted electron

Measurement of v2e dN/d(-) = N (1 + 2v2obscos(2(-))) e - Page 3 <<Reaction Plane Method>> Measure azimuthal angle of each particle with respect to the reaction plane Y dN/d(-) = N (1 + 2v2obscos(2(-))) X Reaction Plane  : azimuthal angle of reaction plane : azimuthal angle of electrons v2obs: strength of azimuthal anisotropy (fitting of dn/d(-) or v2=<cos2(-)>) v2 = v2obs/ σ e - e r.p  wi*sin(2i) tan2  rp =  wi*cos(2i) σ=<cos(2(m-real))> = {<cos(2(A-B))>}1/2

Electron measurement at PHENIX Page 4 Electron measurement at PHENIX The PHENIX experiment has the unique capability to measure electrons at RHIC Electron identification : Cherenkov light in RICH - |h|  0.35 - pt 0.2~4.9 GeV/c Number of hit PMT Ring shape Geometry of PMT -installed North and South side of RHIC. -3 unit rapidity away from mad rapidity Electron identification

Reaction plane Determine r.p using BBC north and south Page 5 Correlation r.p BBC_north & r.p BBC_south r.p resolution <cos(2(A-real))> = {<cos(2(A-B))>}1/2 v2 =v2 obs / resolution Correlation r.p BBC_north & r.p BBC_south Centraryty Determine r.p using BBC central central peripheral Centrality [%]

dn/d distribution Page 6 v2e is corrected by subtracting miss ID of electrons e+(e-) candidate Miss ID e+(e-) -p/2 p/2 cand --- dn/dphi of candidate (detected RICH) e+(e-) miss ID --- dn/dphi of miss ID (dn/d)/N0 1.5 V2e is estimated by subtracting miss ID of electrons 1.0 1.0 dn/d of after subtract Miss ID e+(e-) 0.5 -p/2 p/2 pt 1.0 2.0 3.0 4.0

Pt dependence of v2(e) Page 7 v2 (M.B) pt[GeV/c] Systematic error R.P method (fitting / <cos2()>) electron ID V2e Simulation Photon conversion & Dalitz decay from pi0 It seem like that v2e originating from pi0 is not consistent with v2e which is including all electron sources Electron source Systematic error R.P method (fitting / <cos2()>) electron ID (M.B) pt[GeV/c]

Comparison with v2 of hadrons Page 8 v2 <<Low pt (pt<1.0GeV/c)>> v2(e) is larger than v2(pion)& v2 (proton) -> dominant pi0 decay - small decay angle - decay from higher pt v2 pion & v2 proton : nucl-ex/0305013 (PHENIX) v2 (proton) v2 (pion) v2(e) <<High pt (pt>2.0GeV/c)>> v2(e) seems like smaller than v2 (pion) Particular interest because of the contributions from heavy flavor (M.B) particular interest because of the contributions from heavy-quark (c/b) decays !(but the data include another sources now) (M.B) pt[GeV/c]

What is needed to estimate charmed electron v2 ? Page 9 What is needed to estimate charmed electron v2 ? Relative charm yield to the inclusive electron yield at Run2 (r= Np/Ne) electrons v2 originating photonic source Study v2 D->eX (due to large Q value) R=Nc/Ne

Summary Page10 Azumithal anisotropy of inclusive electrons/positrons are measured with respect to the reaction plane in 200 GeV Au+Au collision at RHIC-PHENIX. v2(e) is larger than v2 (pion) & v2 (proton) at low pt. v2(e) seems like smaller than v2 (pion) at high pt Next Run (Au+Au) will start soon. much more statistics (error bars will be much smaller)