MODELING PION FLOW IN A 139 La + 139 La COLLISION Daniel

39 Dan graduated from Hope College in May 2001 with a Bachelor of Science in Physics. This research was begun in the summer of his sophomore years as part of a NSF Research Experience for Undergraduates and was independently continued in his senior year. Dan is currently attending the graduate program in acoustics at the Pennsylvania Sate University, and is working towards his Ph.D. In his free time, Dan enjoys song writing, playing the guitar and drawing. ABSTRACT This study focused on the flow behavior of pions created in a 139 La + 139 La nuclear collision. The system was simulated and studied at beam energies of 400 MeV/A and 1200 MeV/A using the Boltzmann-Uehling-Uhlenbeck (BUU) transport model for nuclear collisions. The dependence of flow on centrality, the size of the impact parameter, was examined for both beam energies. The dependence of flow on the nuclear equation of state, as well as on Coulomb interactions, was studied. At 400 MeV/A, both positive and negative pions were found to exhibit flow for central (small) impact parameters and anti-flow for peripheral (large, on the size of the nuclear radius) impact parameters. Similar results were obtained at 1200 MeV/A, agreeing with previous experimental data. The predicted flow was insensitive to the choice of equation of state and the Coulomb interactions did not have any profound change on the pion behavior. INTRODUCTION When two nuclei collide, the interactions between them push nucleons away from the collision zone. Examining how particles flow away from this region provides information on the interactions experienced during the collision. In low-energy collisions, the short-range attractive component of the nuclear force causes the nuclei to rotate and be pulled around each other (Figure 1). In high-energy collisions, the nuclei scatter elastically due to the repulsive hard core of the nuclear force (Figure 1). With this knowledge, the nuclear interaction, or the nuclear equation of state (EoS), can be studied. The EoS is used to model interactions between particles. If we think of particles as being connected by springs, then in a stiff EoS, the particles would be connected by stiff springs; in a soft EoS, the particles would be connected by more flexible springs.