A four-gap glass-RPC time-of-flight array with 90 ps time resolution

In this paper, we describe the performance of a prototype developed in the context of the ALICE time-of-flight research and development system. The detector module consists of a 32-channel array of 3/spl times/3 cm/sup 2/ glass resistive plate chamber (RPC) cells, each of which has four accurately spaced gaps of 0.3 mm thickness arranged as a pair of double-gap resistive plate chambers. Operated with a nonflammable gas mixture at atmospheric pressure, the system achieved a time resolution of 90 ps at 98% efficiency with good uniformity and moderate crosstalk. This result shows the feasibility of large-area high-resolution time-of-flight systems based on RPCs at affordable cost.