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Measurement of elliptic flow of electrons from heavy flavor decays @ RHIC Shingo Sakai (Univ. of Tsukuba / JSPS)

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2 outline Introduction Elliptic flow (v 2 ) & Nuclear modification factor (R AA ) Motivation Result Method electron v2 from (Mim. & centrality) Charm v2 (compare model) v 2 vs. R AA Summary

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3 Elliptic flow (v 2 ) ｘ ｙ pｘpｘ pｙpｙ Initial spatial anisotropy Momentum space anisotropy of particle emission 2 th harmonic of the Fourier expansion of the azimuthal distribution Reflect initial spatial anisotropy transfer => A powerful probe of the initial state of the high energy heavy ion collision hydrodynamical interruption => pressure gradient of early stage of collision dN/dφ ∝ N 0 (1+2v 2 cos(2(φ))

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4 Elliptic flow vs. hydro model Identified particle v2 => show mass dependence v2(π) > v2(K) > v2(p) hydrodynamical model well represent the feature of v 2 early time thermalization τ ~ 0.6 fm/c perfect fluid (no viscosity) The matter is like fluid

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5 Nuclear modification factor ; R AA Yield AuAU Yield pp * R AA = particle production @ high pT => hard process => scale by pp collision (R AA = 1.0) significant suppression in AuAu parton energy loss in the dense dense matter

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6 Quark number scaling Presented by M. Lamont (QM04) Baryon Meson v2 is scaled with number of quarks quark level elliptic flow Consistent Quark coalescence model (N.Q.S) N.Q.S well explain other measurement ; Rcp, particle ratio (p/π)

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7 Motivation ; why charm quark ? flow ? energy loss ? Light quarks (u,d,s) flow & energy loss in the matter Charm is much heavier than u,d,s quarks and believed to be produced in initial collisions via gluon fusion => propagates through medium created in the collisions Charm interact medium ? => charm energy loss & charm flow ? => if so, indicate strongly coupling in the medium

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8 Charm study @ PHENIX experiment PHENIX study charm quark via electron,μ and J/ψ Central arm (|η| < 0.35) semi-leptonic decay c -> D -> e cc -> J/ψ -> ee Muon Arm (1.15 < |η| < 2.25) semi-leptonic decay c -> D ->μ cc -> J/ψ-> μμ

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9 Charm quark study via electron Electron sources photonic - photon conversion - Dalitz decay (π 0,η,ω ---) non-photonic - Ke3 decay - primarily semi-leptonic decay of mesons containing c & b background subtraction method cocktail method converter method B.G

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10 Cocktail method estimate background electron with simulation sum up all background electrons Input π 0 (dominant source) use measured pT @ PHENIX other source assume mt scale of pi clear enhancement of inclusive electron w.r.t photonic electron

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11 Converter method install “photon converter ” (brass ;X 0 = 1.7 %) around beam pipe increase photonic electron yield Compare electron yield with & without converter experimentally separate Non-converter ; N nc = N γ +N non-γ Converter ; N c = R *N γ +N non-γ

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12 Charm quarks energy loss clear suppression @ high pT in more central collision => charm quarks energy loss low pT is consistent with binary scaling in large uncertainty Charm interact medium @ low pT ? v2 measurement give us answer

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13 Non-photonic electron v 2 measurement Non photonic electron v 2 is given as; dN e /d = dN pho.e /d + dN non-pho.e /d v 2 e = ( v2 γ e + R NP v2 non-γ e ) / (1 + R NP ) Photonic electron v 2 => Cocktail method (simulation) => Converter method (experimentally determined) Inclusive electron v 2 => Measure (Non-photonic e) / (photonic e) => measure

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14 Electron v2 measurement @ PHENIX e-e- Electron v 2 is measured by R.P. method R.P. --- determined with BBC Tracking (pT,φ) --- DC + PC electron ID --- RICH & EMCal dN/d( - ) = N (1 + 2v 2 obs cos(2( - ))) eID @ RICH B.G. After subtract B.G. Fig : Energy (EMcal) & momentum matching of electrons identified by RICH. Clear electron signals around E-p/p = 0

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15 Inclusive & photonic electron v2 Inclusive e v 2 Photonic e v 2 50 % of electrons come from non-photonic @ high pT (>1.5 GeV/c) photonic electron v2 ; converter (pT 1.0)

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16 Non-photonic electron v2 clear non-zero non-photonic electron v2 measured ! main source of non-photonic electron ; D->e => D v2 is also non-zero

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17 Non-photonic electron v 2 (centrality dep.) Hydro -> driving force of v2 is pressure gradient (ΔP) ΔP is get large with impact parameter (centrality) => v2 get large with centrality Non-photonic electron v 2 seems like get large with impact parameter

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18 expected D v 2 from non-photonic e v 2 expected D meson v2 from non-photonic electron v2 => would be smaller than pi v2 expected D v 2 from non-γ v 2 process (1) D v 2 = a*f(pT) a ; free parameter f(pT) ; pi,K,p (2) D -> e v 2 (3) Calculate χ 2 (4) Find χ 2 minimum for “a”

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19 Charm quark flow ? 12304 pT[GeV/c] Compared with quark coalescence model prediction. with/without charm quark flow (Greco, Ko, Rapp: PLB 595 (2004) 202) - No Bottom contribution - c v 2 small u v 2 @ low pT - quark v 2 flat @ high p T Below 2.0 GeV/c ; consistent with charm quark flow model. => indicate charm quark flow !

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20 Non-γ e v 2 vs. R AA (1) Origin of v2 @ high pT => energy loss pi0 yield strongly suppress @ high pT and strong elliptic flow observed Non-γelectron strongly suppress @ high pT same as pi0 but v2 is smaller than pi0

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21 Non-γ e v 2 vs. R AA (2) estimate D meson v2 assume charm & u have same v2 D meson v2 get N.Q.S mass effect for N.Q.S v2 M (p T ) = v2 1 (R 1 p T ) + v2 2 (R 2 p T ) R i = m i / m M (mi ; effective mass of quark i) (Phys.Rev. C68 (2003) 044901 Zi-wei & Dence Molnar) v2 D (pT) ~ v2 u (1/6*p T ) + v2 c (5/6*p T ) pi0 v 2 u quark v 2

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22 Non-γ e v 2 vs. R AA (3) if charm & u has same v2, the maximum v2 = 0.1 => Non-photonic electron v2 is smaller than pi (pi0) v2 though R AA is consistent with pi0

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23 Summary Study charm v2 via electron v2 measurement Non-zero non-photonic electron v2, decay electron v2 from charm, observed. Non-photonic electron v2 consistent with charm flow model Charm quark study via electron indicate charm flow & charm energy loss in the matter => indicate particles in the matter strongly coupling

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24 Outlook for heavy flavor v 2 study @ PHENIX single μ v 2 new reaction plane detector good resolution => reduce error from R.P. J/ψ v 2 & high pT non-photonic electron v 2 silicon vertex detector direct measurement D meson v 2 [Reaction plane detector] [Silicon vertex detector]

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