Performance of a fast, highly segmented electromagnetic calorimeter

We present results from beam tests of a fast, finegrained electromagnetic calorimeter. This work was part of a program of research and development of detectors suitable for use at the Superconducting Supercollider (SSC). Our research was motivated specifically by a conceptual design of an SSC experiment dedicated to the measurement of muons produced in high-energy p ro ton -p ro ton collisions [1]. In such an experiment it is natural to consider the use of a thick absorber around the interaction point to filter muons from the intense flux of secondary hadrons. However, the correct interpretation of events containing muons may require knowledge of the other, coproduced particles, and one is led inevitably to consider some instrumentation of the absorber to measure the energy flow associated with these additional particles. The use of proportional-wire technology for such absorber instrumentation has a number of attractions [2]. In particular, it is cheap and provides for the possibility of measuring simultaneously the location, direction, and energy of showering particles. The SSC environment is characterized by very high particle production rates and intense radiation levels [3]. Previous work [4] has shown that proport ional wire chambers using small cells, fast gases, special pulse-shaping electronics, and operated at modest gas gains, can perform adequately in this environment. To evaluate some of the concepts outlined above, we have constructed and tested a fine-grained electromagnetic calorimeter which could be attached to the frontend of a hadron absorber. Such a calorimeter could also be employed in any high-rate experiment that requires the precise location and direction of showering particles. The performance of the calorimeter was investigated with high-energy electrons provided by the Tagged Photon Laboratory at Fermilab [5]. Measurements were made with two different electronic readout systems at beam energies of 10, 25, 50, 100, and 200 GeV. The main goal of the beam tests was to learn the dependence of energy and angular resolutions on gas gain and readout speed.