A Photon Multiplicity Detector for the ALICE Experiment

We describe the basic characteristics of a preshower photon multiplicity detector. The event-by-event fluctuation in the detected N<SUB>gamma</SUB>/N<SUB>ch</SUB> is less than 3% for central events of VENUS event generator compared to 2.3% value for the raw event generator, suggesting excellent sensitivity of the detector to study isospin fluctuations. Detector performance can be optimised using both silicon and gas as the sensitive medium. The preshower signal shows good sensitivity to provide estimates of transverse e.m. energy.