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Measurement of elliptic flow of electrons from heavy flavor decays @ RHIC

Measurement of elliptic flow of electrons from heavy flavor decays @ RHIC. Shingo Sakai (Univ. of Tsukuba / JSPS). outline. Introduction Elliptic flow (v 2 ) & Nuclear modification factor (R AA ) Motivation Result Method electron v2 from (Mim. & centrality) Charm v2 (compare model)

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Measurement of elliptic flow of electrons from heavy flavor decays @ RHIC

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

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

  3. pｙ ｙ pｘ ｘ Elliptic flow (v2) • 2th 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 Initial spatial anisotropy dN/dφ ∝ N0(1+2v2cos(2(φ)) Momentum space anisotropy of particle emission

  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 v2 • early time thermalization τ ~ 0.6 fm/c • perfect fluid (no viscosity) • The matter is like fluid

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

  6. Presented by M. Lamont (QM04) Baryon Meson Quark number scaling • 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)

  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

  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

  9. Charm quark study via electron • Electron sources • photonic - photon conversion - Dalitz decay (π0,η,ω ---) • non-photonic - Ke3 decay - primarily semi-leptonic decay of mesons containing c & b • background subtraction method • cocktail method • converter method B.G

  10. Cocktail method • estimate background electron with simulation • sum up all background electrons • Input • π0(dominant source) use measured pT @ PHENIX • other source assume mt scale of pi • clear enhancement of inclusive electron w.r.t photonic electron

  11. Converter method • install “photon converter ” (brass ;X0 = 1.7 %) around beam pipe • increase photonic electron yield • Compare electron yield with & without converter • experimentally separate Non-converter ; Nnc = Nγ+Nnon-γ Converter ; Nc = R *Nγ+Nnon-γ

  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

  13. Non-photonic electron v2 measurement • Non photonic electron v2 is given as; dNe/d = dNpho.e /d + dNnon-pho.e /d v2e = ( v2γe + RNP v2non-γe ) / (1 + RNP) Inclusive electron v2 =>Measure (Non-photonic e) / (photonic e) => measure Photonic electron v2 => Cocktail method (simulation) => Converter method (experimentally determined)

  14. e- Electron v2 measurement @ PHENIX • Electron v2 is measured by R.P. method • R.P. --- determined with BBC • Tracking (pT,φ)--- DC + PC • electron ID --- RICH & EMCal dN/d(-) = N(1 + 2v2obscos(2(-))) eID @ RICH After subtract B.G. B.G. Fig : Energy (EMcal) & momentum matching of electrons identified by RICH. Clear electron signals around E-p/p = 0

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

  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

  17. Non-photonic electron v2 (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 v2 seems like get large with impact parameter

  18. expected D v2 from non-photonic e v2 • expected D v2 from non-γ v2 • process (1) D v2 = a*f(pT) a ; free parameter f(pT) ; pi,K,p (2) D -> e v2 (3) Calculate χ2 (4) Find χ2 minimum for “a” • expected D meson v2 from non-photonic electron v2 => would be smaller than pi v2

  19. Charm quark flow ? • Compared with quark coalescence model prediction. with/without charm quark flow (Greco, Ko, Rapp: PLB 595 (2004) 202) - No Bottom contribution - c v2 small u v2 @ low pT - quark v2 flat @ high pT • Below 2.0 GeV/c ; consistent with charm quark flow model. => indicate charm quark flow ! pT[GeV/c] 0 1 2 3 4 pT[GeV/c]

  20. Non-γ e v2 vs. RAA(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

  21. Non-γ e v2 vs. RAA(2) • estimate D meson v2 assume charm & u have same v2 • D meson v2 get N.Q.S • mass effect for N.Q.S v2M (pT) = v21 (R1 pT) + v22 (R2pT) Ri = mi / mM (mi ; effective mass of quark i) (Phys.Rev. C68 (2003) 044901 Zi-wei & Dence Molnar) v2D(pT) ~ v2u (1/6*pT) + v2c (5/6*pT) pi0 v2 u quark v2

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

  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

  24. Outlook for heavy flavor v2 study @ PHENIX • single μ v2 • new reaction plane detector • good resolution => reduce error from R.P. • J/ψ v2 & high pT non-photonic electron v2 • silicon vertex detector • direct measurement D meson v2 [Reaction plane detector] [Silicon vertex detector]

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