A measurement of charged particle ratios at high transverse momentum in an ultra-relativistic heavy ion collision

Ultra-relativistic heavy ion collisions taking place at RHIC are thought to create conditions favorable for the creation of a quark gluon plasma (QGP). It is the main goal of the Relativistic Heavy Ion Collider (RHIC) to create and provide a definitive characterization of the quark-gluon plasma believed to be created in high energy heavy ion collisions. A determination of the initial conditions leading to the formation of a QGP is an important part of understanding its properties. Information about the evolution of the system formed during a heavy ion collision can be obtained by investigating charged particle ratios. The charged pion and kaon particle ratios as well as the anti-proton-to-proton ratio have been measured at high transverse momentum using a RICH detector, Comparisons have been made to previous measurements made with smaller collision systems and are found to be consistent with expectations derived from these smaller systems. The transverse momentum dependence of the charged particle ratios is consistent with being constant over the range measured, 0.75 < p_⊥[GeV/c] < 2.5 and can be described within a thermodynamical model of the collision and is an indication that chemical equilibrium was achieved over the course of the collision.