Elliptic Flow of Inclusive Photon Elliptic Flow of Inclusive Photon Ahmed M. Hamed Midwest Critical Mass University of Toledo, Ohio Oct. 22, October, 2005 Wayne State University

Outline: Outline. Motivation. Analysis details and technique. Data and results. Discussion. Conclusion Oct. 22,2005

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. * 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 =

Higher harmonics flow Partonic collectivity or Hadronic collectivity! Partonic collectivity or Hadronic collectivity! V 1 <0 V2<0V2<0 Anisotropic flow Directed flow Elliptic flow Correlations w.r.t the reaction plane Overall shift in the transverse plane V 1 >0 V2>0V2>0 * 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  )+…] v 2 is a measure of interactions in the system v 2 is a measure of interactions in the system v 2 = Flow Radial/Isotropic flow V 1 =0 x y V2=0V2=0 x y Azimuthal Distribution v n = Motivation: v 2 How?

solid: STAR open: PHENIX PRL91(03) Partonic collectivity is an expected attribute of a QGP Motivation: V 2 Result

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

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. * 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. * QGP potentially detectable via thermal photon radiation: Thermal photons dominantly from early, hot QGP phase initial temperature.

Motivation: Photons result *  0 ’s suppressed going to central collisions. *  0 ’s suppressed going to central collisions. * Direct photons consistent with NLO pQCD “binary scaling”. * Direct photons consistent with NLO pQCD “binary scaling”. *  0 suppression caused by medium created in A+A collisions. *  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 p T and centrality dependences of  0 and inclusive  V 2 is consistent with that of other mesons. * The V 2 of inclusive  is consistent with The V 2 of  from hadronic decays. * The V 2 of inclusive  is consistent with The V 2 of  from hadronic decays. Consistent with no direct photon signal. * Implementation of V 2 =0 for direct photons in p T (4-6GeV/C). * Implementation of V 2 =0 for direct photons in p T (4-6GeV/C).

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) R.J.Fries, B. Muller and D.K.Srivastava, Phys.Rev. Lett. 90, (2003) Suppression B.G. Zakharov, JETP Lett. 80, 1 (2004) 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.

STAR TPC and FTPC to reconstruct the event plane 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

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 / 

Data and results : s=  200 GeV. Run IV. 10.2M events. Event plane

Data and results: BEMC Uniformity-Minimum Bias.

Data and results: BEMC Uniformity-High Tower.

Data and results: V 2

Discussion * At low E T (E T <2GeV), The E T dependences of inclusive  V 2 is consistent with that of other mesons which indicate the dominance of  0 in that range. * At Intermediate E T, the V2 reaches its maximum at ~ 3GeV which is consistent with that of other hadrons. * At Intermediate E T, the V2 reaches its maximum at ~ 3GeV which is consistent with that of other hadrons. * At High E T, the present produced statistics is small.

Conclusion * The azimuthal anisotropy is a powerful tool to study the early stage of ultra-relativistic nuclear collision. * The azimuthal anisotropy is a powerful tool to study the early stage of ultra-relativistic nuclear collision. * Partonic collectivity is confirmed. * Direct photon is one of the most promising signature of QGP. * No Direct photon signal is observed. * Hadron suppression at high p T is a final state effect. * Direct photons consistent with NLO pQCD “binary scaling”. * 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 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. * The V 2 measurement of direct photons would provide more information on the dynamic and properties of the produced hot and dense matter.

The End, Thank You The End, Thank You