09/15/10Waye State University1 Elliptic Flow of Inclusive Photon Ahmed M. Hamed Midwest Critical Mass University of Toledo, Ohio October, 2005 Wayne State University

09/15/10Waye State University2 Outline: Outline. Motivation. Analysis details and technique. Data and results. Discussion. Conclusion

09/15/10Waye State University3 Elliptic flow can provide early time information on the collectivity of particles from Heavy-ion collisions: * Non-Central AA collisions result in an azimuthally anisotropic distribution of particles in coordinate-space. * Density gradients and interactions between the particles lead to an Asymmetry in momentum-space. * Signal is self-quenching with time-EARLY TIME OBSERVABLE! Motivation: v 2 Why? Reaction plane Out-of-plane In-plane  = V 2 =

09/15/10Waye State University4 Higher harmonics flow Partonic collectivity or Hadronic collectivity! V 1 <0 V 2 <0 Anisotropic flow Directed flow Elliptic flow Correlations w.r.t the reaction plane Overall shift in the transverse plane V 1 >0 V 2 >0 v 2 is a measure of interactions in the system v 2 = * Expanding in Fourier series: E(d 3 N/d 3 P)=1/  (d 2 N/d 2 p T dy)[1+2v 1 cos(  )+2 v 2 cos(2  )+…] Flow Radial/Isotropic flow V 1 =0 x y V 2 =0 x y Azimuthal Distribution v n = Motivation: v 2 How?

09/15/10Waye State University5 solid: STAR open: PHENIX PRL91(03) ‏ Partonic collectivity is an expected attribute of a QGP Motivation: v 2 Result

09/15/10Waye State University6 Direct Real Photons: Non-Thermal photons: 1. Prompt photons. 2. Pre-equilibrium photons. Thermal photons: 1. QGP photons. 2. Hadron gas photons. Background Photons: Compton-like Annihilation Bremsstrahlung Hadron decay, etc. Turbide, Rapp, Gale, Phys. Rev. C 69 (014903), 2004 Realistic Calculation Motivation: which Photons? hard : Thermal Schematic Photon Spectrum Decay photons

09/15/10Waye State University7 Motivation: Why Photons? p+p collisions: * Test of QCD. * Constraining gluon distribution functions. * In polarized p+p also gluon spin structure function. A+A collisions: # Photons don’t strongly interact with fireball. * Carry information about early stage of collision. # Direct Photons at high p T * Allow test of binary scaling for hard processes. * Important for interpretation of high-p T hadron suppression at RHIC. * QGP potentially detectable via thermal photon radiation: Thermal photons dominantly from early, hot QGP phase initial temperature.

09/15/10Waye State University8 Motivation: Photons result *  0 ’s suppressed going to central collisions. * Direct photons consistent with NLO pQCD “binary scaling”. *  0 suppression caused by medium created in A+A collisions. PHENIX preliminary * The p T and centrality dependences of  0 and inclusive  v 2 is consistent with that of other mesons. * The measured v 2 of inclusive  is consistent with the v 2 of  from hadronic decays. * v 2 =0 for direct photons.

09/15/10Waye State University9 Motivation: v 2 of inclusive photons Why? * “Jet quenching” photons. Enhancement R.J.Fries, B. Muller and D.K.Srivastava, Phys.Rev. Lett. 90, (2003)‏ Suppression B.G. Zakharov, JETP Lett. 80, 1 (2004)‏ Bremsstrahlung Scattering What is the origin of the binary scaling of direct photon? * Thermal Photons. Enhancement Summary: * Measuring v 2 of Direct photons: -Help to disentangle the different production mechanism of direct photon. * STAR can probe for further higher transverse energy. * v 2 of inclusive photon is the first step toward v 2 of direct photon. Coulomb and Annihilation: v 2 =0 Scattering: v 2 >0 Similar to hadrons Bremsstrahlung: v 2 <0 -Thermal photons reflect the dynamical evolution of the formed matter. * At very high P T v 2 will be dominated by direct photon due to the large suppression of  0.

09/15/10Waye State University10 STAR TPC and FTPC to reconstruct the event plane 0<pt<2GeV/C, |z| 15 -1<  <0 TPC 2.6<  <4.0 FTPC, Number of tracks> Towers 0.05  <  <1,0<  <2 ,  E=0.16  E STAR BEMC Analysis details and technique Energy Threshold: Minimum Bias: >0.1GeV High Tower: >3GeV

09/15/10Waye State University11 Analysis details and technique * Event plane reconstruction: 2  EP = atan2 (  i sin2  1 i +  i sin2  2 i,  i cos2  1 i +  i cos2  2 i )‏ 2  EP = atan2 (  i sin2  w1 i +  i sin2  w 2 i +  i sin2  E1 i +  i sin2  E 2 i,  i cos2  w 1 i +  i cos2  w 2 I +  i cos2  E 1 i +  i cos2  E 2 i )‏ TPC: FTPC: * Event plane recentering: sin2  cos2  sin2  - M  sin2  / M  cos2  - M  cos2  / M  M: number of tracks in each sub-event * Check the uniformity of BEMC. * Correlating inclusive photon with event plane: v 2 =  cos(2  - 2  EP )  * Correction for event plane resolution: v 2 Real = v 2 Observed / 

09/15/10Waye State University12 Data and results : s=  200 GeV. Run IV. 10.2M events. Event plane

09/15/10Waye State University13 Data and results: BEMC Uniformity-Minimum Bias.

09/15/10Waye State University14 Data and results: BEMC Uniformity-High Tower.

09/15/10Waye State University15 Data and results: v 2

09/15/10Waye State University16 Discussion - The E T dependences of inclusive  v 2 is consistent with that of other mesons which indicate the dominance of  0 in that range. - The v 2 reaches its maximum at ~ 3GeV which is consistent with that of other hadrons. * At low E T (E T <2GeV): * At intermediate E T : - Nice matching between the minimum bias and high towers data. * At High E T : - The present produced statistics is small, however the measurements indicate that the v 2 has non-zero value.

09/15/10Waye State University17 Conclusion * The azimuthal anisotropy is a powerful tool to study the early stage of ultra-relativistic nuclear collision. * Direct photon is one of the most promising signature of QGP. * No Direct photon signal is observed yet in the available p T range. * At very high P T, v 2 will be dominated by direct photon due to the large suppression of  0. * The v 2 measurement of direct photons would help to disentangle the various scenarios of direct photon production. * The v 2 measurement of direct photons would provide more information on the dynamic and properties of the produced hot and dense matter. * Measurement of  0 can reach very high pT and thus should permit study of the effect of hard processes, e.g. jet quenching, on v 2.

09/15/10Waye State University18 The End, Thank You