electron photon flow Elliptic flow measurement of direct

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

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/2006 Kentaro MIKI 2

1 -1. initial probe of collisions Elliptic flow - the probe of early stage The collision participation part in the early stage has spatial anisotropy. z Pressure gradient is largest in the shortest direction of the ellipsoid. Emission particles reflect initial spatial anisotropy transfer. x -Elliptic flow (v 2) is defined by the 2 nd coefficient of Fourier expansion 2 nd harmonic amplitude : v 2 : azimuthal angle of particles : azimuthal angle of reaction plane 24/Nov/2006 Kentaro MIKI |fi- n| 3

1 -2. particles from collisions several particles emitted from nuclear collisions Time Space-time Evolution of A+A collision m g Jets p K K 0* f W e freeze-out 16 fm/c hadron gas 8 fm/c mixed phase 4 fm/c equilibrated QGP hadron … 0. 6 fm/c electron … Space (z) A A photon … Elliptic flow were measured at each particles in PHENIX. 24/Nov/2006 Kentaro MIKI 4

1 -3. Elliptic Flow (hadron) What have we learned from anisotropic flow of hadron v 2 scales approximately with the number of valence quark of hadrons 24/Nov/2006 indicate partonic level flow of , K, and proton Kentaro MIKI 5

1 -4. Elliptic Flow (electron) What have we learned from Anisotropic Flow of electron Electron sources charm decay beauty decay Dalitz decay Di-electron decay photon conversion Kaon decay Thermal dileptons non photonic electron Compared with quark coalescence model prediction. (1) Consistent with c thermal [Phys. Lett. B 595 202 -208 ] (2) large cross section ; ~10 mb [PRC 72, 024906] consistent with charm quark flow model below 2 Ge. V/c. indicate charm quark flow 24/Nov/2006 Kentaro MIKI 6

2 -1. 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/2006 Kentaro MIKI 7

2 -2. definition of Direct photon all remaining photons after subtraction of all hadron decay photons 0 hadron decay photon thermal photon prompt photon jet fragment photon direct photon 24/Nov/2006 hadron decay photon Kentaro MIKI 8

2 -3. Direct photon invariant yield Invariant yield of direct photon in PHENIX thermal window prompt photon 24/Nov/2006 -> 1~3 Ge. V/c (? ) -> 6~ Ge. V/c (? ) Kentaro MIKI direct photon invariant yield Good agreement with Ncoll scaled p. QCD. 9

2 -4. Nuclear modification factor Double ratio : inclusive / background -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 24/Nov/2006 Kentaro MIKI 10

3 -1. Direct photon v 2 motivation ! We attempt to measure the azimuthal anisotropy of direct photon two initial probes combine + v 2 --- reflect the shape + direct photon --- reflect the properties 24/Nov/2006 Kentaro MIKI of particle emission source 11

3 -2. Direct photon v 2 is equal to 0 ? or not ? prompt photon jet fragment photon v 2 = 0 thermal photon v 2 > 0 annihilation compton scattering Bremsstrahlung (energy loss) 24/Nov/2006 Thermal photon (HG+QGP): v 2 R. Chatterjee et al. nucl-th/0511079 v 2 < 0 Kentaro MIKI 12

4 -1. How to measure hadron decay photon ? inclusive photon hadron decay back ground direct photon 0, , … hadron decay back ground measurement invariant mass distribution of 2 1. 0~3. 0~5. 0~10. 0 d distribution at each p. T bin hadron decay contamination 24/Nov/2006 Kentaro MIKI 13

4 -2. How to measure direct photon v 2 ? direct photon v 2 = inclusive photon v 2 - hadron decay back ground v 2 (with their weight) v 2 0 v 2 p. T [Ge. V/c] Double ratio v 2 inclusive photon v 2 24/Nov/2006 p. T [Ge. V/c] Kentaro MIKI p. T [Ge. V/c] 14

4 -3. back ground and inclusive photon compared hadron decay photon v 2 and inclusive photon v 2 centrality 00 to 92 % √s. NN = 200 Ge. V Au+Au collisions hadron decay photon v 2 inclusive photon v 2 subtracted photon (PHENIX preliminary) subtracted photon (previous analysis result) 24/Nov/2006 Kentaro MIKI 15

5 -1. 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/2006 Kentaro MIKI 16

5 -2. result ~ direct photon v 2 ~ We compared to another v 2 analysis and modification factor. line : total error PHENIX preliminary - Direct photon v 2 seems to zero within error bar in high p. T. -> It is consistent to the result of RAA analysis. - Direct photon v 2 may be non zero in 3 to 4 Ge. V/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. 24/Nov/2006 Kentaro MIKI 17

5 -3. result ~ non-photonic electron v 2 and RAA~ We compared to v 2 and RAA at non-photonic electron. RAA -> 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/2006 Kentaro MIKI 18

6 -1. Next step … Direct photon v 2 need more accuracy to do discussion as the initial probe of collisions. - more statistics ? - another method ? theoretical curve of thermal photon Thermal photon (HG+QGP): v 2 R. Chatterjee et al. nucl-th/0511079 Now, we are interested in internal conversion method to see the v 2 in middle p. T. 24/Nov/2006 Kentaro MIKI 19

6 -2. internal conversion method Compton q e+ Any source of real produces e- virtual with very low mass g* g q 140 -200 Me. V 200 -300 90 -140 0 -30 24/Nov/2006 Kentaro MIKI 20

6 -3. invariant yield of direct photon Direct photon invariant yield is compared to thermal + p. QCD curve L. E. Gordon and W. Vogelsang Phys. Rev. D 48, 3136 (1993) D. d’Enterria, D. Perresounko nucl-th / 0503054 Data consistent with thermal + p. QCD If we estimate the direct photon v 2 from this method, is the result improved ? it continues … 24/Nov/2006 Kentaro MIKI 21

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 thermal photon effect to v 2. We are determining the internal conversion method as a next step. 24/Nov/2006 Kentaro MIKI 22

Ex. Back up 24/Nov/2006 Kentaro MIKI 23

4 -1. RHIC-PHENIX 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. lead scintillator (Pb. Sc) ・energy resolution 2. 1 8. 1 %/ E 1/2 [Ge. V] | | < 0. 375 24/Nov/2006 lead glass (Pb. Gl) ・energy resolution 0. 76 5. 95 %/ E 1/2 [Ge. V] =90 2 Kentaro MIKI 24

Ex. result ~ “subtracted” photon ~ PHENIX preliminary 24/Nov/2006 PHENIX preliminary Kentaro MIKI 25

Ex. result ~ direct photon v 2 ~ PHENIX preliminary 24/Nov/2006 PHENIX preliminary Kentaro MIKI PHENIX preliminary 26