PHASES OF STRONGLY INTERACTING MATTER IN THE BRAHMS EXPERIMENT

Abstract

We review results obtained by the BRAHMS experiment at the Relativistic Heavy Ion Collider (RHIC) for the systems of Au+Au and Cu+Cu colliding at p sNN = 200 GeV and at 62:4 GeV, and p+p colliding at p sNN = 200 GeV. The observed number of charged particles produced per unit of rapidity in the central rapidity region indicates that a high energy density system is produced at the initial stage of the Au+Au reaction. Analysis of anti-particle to particle ratios as a function of rapidity and collision energy reveal that particle populations at the chemical freeze-out stage for heavy-ion reactions at and above SPS energies are controlled by the baryon chemical potential. We present rapidity dependent p= ratios within 0 < y < 3 for Au+Au and Cu+Cu at p sNN = 200 GeV. The ratios are enhanced in nucleus-nucleus collisions as compared to p+p collisions. The particle ratios are discussed in terms of their system size and rapidity dependence. We compare RAA for Au+Au at p sNN = 200 GeV and at 62:4 GeV, and for Au+Au and Cu+Cu at p sNN = 62:4 GeV.RAA is found to increase with decreasing collision energy, decreasing system size, and when going towards more peripheral collisions. However, RAA shows only a very weak dependence on rapidity (for 0 < y < 3:2), both for pions and protons.