MEASURING GLOBAL OBSERVABLES WITH PHENIX

When the Relativistic Heavy-Ion Collider (RHIC) begins operations, it will be capable of colliding nuclei of various sizes, from protons up to Au, at center-of-mass energies of 200 to 500 GeV per nucleon pair. Some of these collisions are expected to produce a new state of matter, the quark-gluon plasma (QGP), in which quarks are no longer confined to individual hadrons and in which chiral symmetry has been restored. Numerous predictions have been made as to how a phase transition to a QGP would affect the particle spectra produced in these collisions (see, for example, a recent review by Harris and Mueller). The PHENIX physics philosophy is to detect and systematically study the QGP via a simultaneous measurement of many different probes/signatures of the plasma, as a function of the energy density achieved in the nucleus-nucleus collision. To achieve this goal, the PHENIX detector has been designed as a multi-purpose spectrometer, capable of concurrently measuring hadrons, leptons and photons, as well as global properties of the collision, e.g. energy density, as will be detailed below