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

2. 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

3. 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))

4. 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

5. 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

6. 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)

7. 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. 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. 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

10. 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

11. 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

12. 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. 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

14. 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

15. 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)

16. 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. 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

18. 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”

19. 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 !

20. 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

21. 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

22. 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

23. 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. 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]