A stack of two-dimensional multiwire proportional chambers as part of an electromagnetic calorimeter

A set of four multiwire proportional chambers with analog readout were inserted in the calorimeter of the R704 experiment at the CERN ISR. In this experiment, charmonium (cc) resonances were directly formed through pp annihilation. Owing to the high hadronicbackground, only electromagnetic final states (e+e− and γγ) were detected. Located near the maximum of the electromagnetic shower development, the stack of four chambers had as its main purpose a fine spatial localization, together with a good electron-hadron discrimination and multishower rejection in the critical few GeV region.