Can the QGP be found using only an Electromagnetic Calorimeter ?

Measurements using the finely segmented EM Calorimeter in PHENIX are presented. The issue of whether these are sufficient to claim discovery of the Quark Gluon Plasma is discussed. The " gold-plated " signature for the discovery of the Quark Gluon Plasma and the proof of " deconfinement " is the suppression of J/Ψ due to " Debye screening " which dissociates the bound pair of c − ¯ c quarks. [ 1] The PHENIX experiment at RHIC is a special purpose detector [ 2] designed to observe this classic signature, and, more generally, to measure rare processes involving leptons and photons at the highest luminosities. The principles of the design of PHENIX are illustrated in Fig. 1. In order to detect electrons in hadron collisions, where the typical ratio of e ± /π ± is known to be of order of 10 −4 for prompt electrons (from charm) at 23.5 ≤ √ s ≤ 62.4 GeV [ 4] (ISR energies), one must plan on a charged pion rejection of > 10 5. PHENIX decided to use a Ring Imaging Cerenkov counter (RICH) in combination with an Electromagnetic Calorimeter (EMCal) to achieve this rejection. There is also the issue of the huge background of e ± from internal and external conversion of the photons from π 0 decay or from direct photon production, which must be measured and understood to high precision. The EMCal is crucial for this purpose.