Nuclear Theory Seminars at Texas A&M: Spring 2006

Location: Cyclotron Building (434), Seminar Room

Friday, April 28, 2:00pm

Dr. Ahmed Hamed
Toward the elliptic flow of direct photons

Abstract:

The discovery of asymptotic freedom in the theory of the strong interaction has initiated the high-energy heavy-ion collisions program. It is expected to produce a deconfined phase of quarks and gluons in such collisions. The prediction of the phase transition to occur in the vicinity of the non-pQCD regime increases the challenges at the theoretical and experimental level. The Relativistic Heavy Ion collider (RHIC) at Brookhaven National Laboratory is constructed to explore the QGP-hadronic matter phase transition.

The elliptic flow, (v₂), is one of the important characteristics of a thermally expanding fireball created in relativistic heavy ion collisions. Typically, elliptic flow is measured for strongly interacting particles which decouple from the thermal medium at later times. Direct photons, which decouple from the medium upon creation, carry information about the entire fireball evolution, in particular the information about the early QGP stage. We measure the inclusive photons elliptic flow in Au+Au collisions using the STAR BEMC. To reduce the effect of so-called non-flow we use the FTPC to determine the event plane. It is observed that v₂(p_t) decreases at high transverse momentum similar to that of hadrons.

Neutral pions represent almost all the background for the direct photon measurements. In order to reconstruct the neutral pions in the high multiplicity Au+Au collisions environment, we have developed a new cluster finder for the STAR BEMC, which suppresses cluster splitting and allows to see clear neutral pion invariant mass peak at all centralities.

I will present results from the elliptic flow measurements of inclusive photons and the progress in the study of neutral pions productions in Au+Au collisions system.