Study of Resistive Plate Chambers for the Alice dimuon spectrometer

The trigger system of the Alice dimuon spectrometer is based on RPC detectors. We present experimental results of a beam test about rate capability, time resolution and cluster size of single gap RPC detectors operating both in 'streamer mode' and in 'avalanche mode'. We have compared the performances of small chambers (50x50 cm2) built with bakelite of different resistivity, from ∼ 3 · 109 Ωcm to ∼ 3 · 1011 Ωcm. For the low resistivity RPC we obtained a rate capability of several hundreds of Hz/cm2 when it is operating in 'streamer mode', and of several thousands of Hz/cm2 when it is operating in 'avalanche mode'