ALICE dimuon trigger: Overview and electronics prototypes

ALICE is the LHC experiment (2005) dedicated to the study of heavy ion collisions. Amongst the ALICE sub-detectors, the muon spectrometer will investigate the dimuon production from heavy resonance (J/ψ,Υ) decays, which is believed to be a promising signature of the Quark Gluon Plasma (QGP) formation. For maximum efficiency of the spectrometer, a dedicated dimuon trigger is presently built. The detector part itself is based on resistive plate chambers (RPCs) operated in streamer mode and is the topic of another contribution to this conference. This paper gives the principle and the simulated performances of the trigger and is also focussed on the description of the electronics prototypes and future developments. The RPCs are read-out by X and Y orthogonal strips: the front-end chips are presently developed. The signals are sent to the trigger electronics which basically performs a p_t cut on the tracks to reduce the background. A prototype of fast (decision time 200 ns) programmable electronics working in a pipelined mode at 40 MHz has been built and tested. This prototype handles simultaneously 160 digital information from the strips. The tests of the trigger card have required the construction of a pattern generator (160 bits at 40 MHz).