The development of silicon multiplicity detectors for RHIC

A frequently stated common goal of all relativistic heavy ion experiments is the observation of quark-gluon plasma (QGP). This postulated state of matter results from the QCD prediction of a phase transition in hadronic matter at sufficiently high energy densities. Several specific signatures indicating the creation of such a state are theoretically predicted and sought in many experiments. These include large soft photon and lepton production, the suppression of J/ψ production, strangeness enhancement etc. In addition to these specific signatures one or both of two experimental observables are used by most experiments for the global characterization of heavy ion collisions. These are the total produced transverse energy (ET), and the number of the produced charged particles (NCh). Both observables are closely related to thermodynamic variables commonly used in theory to describe the conditions necessary for the formation of such states. The importance of these observables is further enhanced by the fact that it is relatively simple for either one of them to be used at the trigger level in order to tag the centrality of a given interaction. In this development project the authors are using silicon detectors to measure the total number of charged particles produced in a heavy ion collision as well as to measure their production as a function of pseudorapidity. Unless calorimetric coverage over a large solid angle is necessary for other reasons measuring NCh instead of ET is clearly more practical and less expensive