A Multi-strip Multi-gap RPC Barrel for Time-of-Flight Measurements

The FOPI detector [1] at the heavy-ion synchrotron SIS-18 at GSI in Darmstadt has upgraded part of its time-of-flight (ToF) system by adding a new sub-detector shell (called the MMRPC Barrel) that is made out of Multi-strip Multi-gap Resistive-Plate Counters (MMRPCs). The MMRPC Barrel has an active area of 5 m2 covered by 2400 individual anode strips [2] and [3] which are read out at both ends by custom-designed electronics [4] and [5]. With these multi-strip anodes we have obtained an enhanced detector granularity with 95% efficiency and a ToF resolution σToFσToF better than 90 ps which increases the identification limit for charged kaons up to laboratory momenta of at least 1 GeV/c. In this paper we report on the design, construction and operational characteristics of the MMRPC Barrel and describe its performance during the first experiments.