24 Nov 2006 Kentaro MIKI University of Tsukuba “electron / photon flow” Elliptic flow measurement of direct photon in √s NN =200GeV Au+Au collisions at RHIC-PHENIX International Workshop On Hadron Physics and Property of High Baryon Density Matter

24/Nov/2006Kentaro MIKI2 0. outline 1. introduction - elliptic flow (hadron, electron) 2. direct photon analysis - direct photon analysis as the initial probe of collisions 3. direct photon v 2 - Why do we analyze the direct photon v 2 ? 4. method - How to measure ? 5. result - The result of direct photon v 2 at PHENIX 6. next step - internal conversion method 7. summary

24/Nov/2006Kentaro MIKI initial probe of collisions x z  : azimuthal angle of particles  : azimuthal angle of reaction plane Elliptic flow - the probe of early stage -Elliptic flow (v 2 ) is defined by the 2nd coefficient of Fourier expansion  i -  n | 2 nd harmonic amplitude : v 2 The collision participation part in the early stage has spatial anisotropy. Pressure gradient is largest in the shortest direction of the ellipsoid. Emission particles reflect initial spatial anisotropy transfer.

24/Nov/2006Kentaro MIKI particles from collisions Space-time Evolution of A+A collision p K  e   Space (z) Time A A     Jets 0.6fm/c 4fm/c 16fm/c 8fm/c hadron gas mixed phase freeze-out equilibrated QGP hadron … electron … photon … several particles emitted from nuclear collisions Elliptic flow were measured at each particles in PHENIX.

24/Nov/2006Kentaro MIKI Elliptic Flow (hadron) v 2 scales approximately with the number of valence quark of hadrons indicate partonic level flow of , K, and proton What have we learned from anisotropic flow of hadron

24/Nov/2006Kentaro MIKI Elliptic Flow (electron) What have we learned from Anisotropic Flow of electron Compared with quark coalescence model prediction. consistent with charm quark flow model below 2 GeV/c. Electron sources charm decay beauty decay Dalitz decay Di-electron decay photon conversion Kaon decay Thermal dileptons non photonic electron photonic electron indicate charm quark flow (1) Consistent with c thermal (2) large cross section ; ~10 mb [PRC72,024906] [Phys.Lett. B ]

24/Nov/2006Kentaro MIKI Direct photon Direct photon (non hadronic photon) : probe of initial collision Photon have much weaker interactions with other particles and thus preserve information about their creation. Direct photons are one of the most effective probes to study properties of hot dense medium at initial state of heavy ion collisions.

24/Nov/2006Kentaro MIKI definition of Direct photon Direct photon all remaining photons after subtraction of all hadron decay photons prompt photon thermal photon jet fragment photon 00   hadron decay photon direct photonhadron decay photon

24/Nov/2006Kentaro MIKI Direct photon invariant yield Invariant yield of direct photon in PHENIX Good agreement with Ncoll scaled pQCD. thermal window -> 1~3 GeV/c (?) prompt photon -> 6~ GeV/c (?) direct photon invariant yield

24/Nov/2006Kentaro MIKI Nuclear modification factor -Neutral mesons receive strong suppression. -Direct photon is not suppressed in mid to high p T -> Direct photon have original information different from hadron analysis -Strong suppression of neutral mesons makes possible the clear extraction of direct photon signal Double ratio :  inclusive /  background

24/Nov/2006Kentaro MIKI Direct photon v 2 We attempt to measure the azimuthal anisotropy of direct photon two initial probes combine + v reflect the shape + direct photon --- reflect the properties of particle emission source motivation !

24/Nov/2006Kentaro MIKI Direct photon v 2 annihilation compton scattering Bremsstrahlung (energy loss) Direct photon v 2 is equal to 0 ? or not ? prompt photonv 2 = 0thermal photonv 2 > 0 jet fragment photon v 2 > 0 v 2 < 0 Thermal photon (HG+QGP): v 2 R. Chatterjee et al. nucl-th/

24/Nov/2006Kentaro MIKI How to measure hadron decay photon ? inclusive photon hadron decay back ground  0, , … direct photon invariant mass distribution of 2  1.0~3.03.0~5.05.0~10.0 d  distribution at each p T bin hadron decay contamination hadron decay back ground measurement

24/Nov/2006Kentaro MIKI How to measure direct photon v 2 ? inclusive photon v 2 hadron decay back ground v 2 direct photon v 2 =- (with their weight) inclusive photon v 2 p T [GeV/c] v2v2  0 v 2 p T [GeV/c] v2v2 Double ratio

24/Nov/2006Kentaro MIKI back ground and inclusive photon centrality 00 to 92 % √s NN = 200 GeV Au+Au collisions hadron decay photon v 2 inclusive photon v 2 subtracted photon (PHENIX preliminary) subtracted photon (previous analysis result) compared hadron decay photon v 2 and inclusive photon v 2

24/Nov/2006Kentaro MIKI result ~ direct photon v 2 ~ Direct photon v 2 estimated by back ground v 2 subtracted from inclusive photon v 2. They are the result of direct photon v 2 analysis in Au+Au collisions.

24/Nov/2006Kentaro MIKI result ~ direct photon v 2 ~ PHENIX preliminary We compared to another v 2 analysis and modification factor. - Direct photon v 2 seems to zero within error bar in high p T. -> It is consistent to the result of R AA analysis. - Direct photon v 2 may be non zero in 3 to 4 GeV/c region. -> Thermal photon ?? - Direct photon have smaller v 2 than  0 v 2 in high p T. - Direct photon have another value to proton v 2 in high p T. -> This analysis suggest the another information from hadron v 2 analysis. line : total error

24/Nov/2006Kentaro MIKI result ~ non-photonic electron v 2 and R AA ~ We compared to v 2 and RAA at non-photonic electron. R AA -> suppress in the high p T v 2 -> decrease in the high p T These figures indicate the another structure to hadron or photon analysis.

24/Nov/2006Kentaro MIKI Next step … Direct photon v 2 need more accuracy to do discussion as the initial probe of collisions. - more statistics ? - another method ? Now, we are interested in internal conversion method to see the v 2 in middle p T. theoretical curve of thermal photon Thermal photon (HG+QGP): v 2 R. Chatterjee et al. nucl-th/

24/Nov/2006Kentaro MIKI internal conversion method Compton q  g q e+e+ e-e MeV Any source of real  produces virtual  with very low mass

24/Nov/2006Kentaro MIKI invariant yield of direct photon Direct photon invariant yield is compared to thermal + pQCD curve L.E.Gordon and W.Vogelsang Phys. Rev. D48, 3136 (1993) D. d’Enterria, D. Perresounko nucl-th / Data consistent with thermal + pQCD If we estimate the direct photon v 2 from this method, is the result improved ? it continues …

24/Nov/2006Kentaro MIKI22 7. summary Azimuthal Anisotropy of direct photon are estimated in PHENIX. Direct photon v 2 is equal to zero within error bar in high p T region. Direct photon v 2 maybe have centrality dependence. In the future, this v 2 are measured at more accuracy in inter-mediate p T. It is possibility to see the thermal photon effect to v 2. We are determining the internal conversion method as a next step.

24/Nov/2006Kentaro MIKI23 Ex. Back up

24/Nov/2006Kentaro MIKI RHIC-PHENIX lead scintillator (PbSc) ・ energy resolution 2.1  8.1 %/ E 1/2 [GeV] lead glass (PbGl) ・ energy resolution 0.76  5.95 %/ E 1/2 [GeV] RHIC The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory is a world class scientific research facility that began operation in 2000, following 10 years of development and construction. |  | <  =90  2

24/Nov/2006Kentaro MIKI25 Ex. result ~ “subtracted” photon ~ PHENIX preliminary

24/Nov/2006Kentaro MIKI26 Ex. result ~ direct photon v 2 ~ PHENIX preliminary