A dual threshold technique to improve the time resolution of resistive plate chambers in streamer mode

The trigger setup of the dimuon arm of ALICE, the dedicated Heavy-Ion Experiment at LHC, is based on Resistive Plate Chambers (RPCs). This gaseous detector can be operated either in streamer or in avalanche mode, each mode having its own advantages and drawbacks. Using conventional discrimination techniques, like single threshold or constant fraction discriminator, the time resolution is better in avalanche mode (commonly 1 ns) unless the RPC is operated in streamer mode at quite high running voltages which is not suitable. Since we propose to operate the RPCs in streamer mode in ALICE, we have studied a new discrimination technique in order to improve the time resolution in this mode. With this method, a comparable timing quality as one of the avalanche modes is typically obtained, as soon as the applied voltage is sufficient for the RPC to reach the full efficiency. This is an important progress not only for the ALICE trigger but also because the RPC detector is widely used in streamer mode. (C) 2001 Elsevier Science B.V. All rights reserved.