SINGLE-SIDED MU-STRIP DETECTOR WITH BACKPLANE READOUT FOR FAST TRIGGER APPLICATIONS

Motivated by a project to trigger on the charged decay of neutral stra nge particles, a single-sided Si-mu-strip vertex detector (SVX) has be en placed in vacuum close to the liquid hydrogen target of the Crystal Barrel spectrometer at LEAR (CERN). An event is accepted if the multi plicity of charged tracks outside the SVX increases by 2 or more. For this purpose the signals from the detector backplane are read out by e lectronics specially adapted to the problems of speed, high detector c apacitance and high leakage current. This provides a fast first level trigger (0.5 mu s), gives an additional energy deposit measurement and helps in pile up recognition. The exact event multiplicity for a seco nd level trigger can be determined from discriminators in the strip si gnal ADCs during the serial readout (26 mu s), using a CAMAC based mul tiplicity encoder. If no digital control signals are applied to the SV X, the signal-to-noise ratio for minimum ionising particles (MIPs) on the backplane has been measured to be around 12, in good agreement wit h noise calculations, where noise cross-talk between the two preamp sy stems is neglected. The backplane signal provides, moreover, an intrin sic trigger for the readout of the strip side, allowing for instance t he detection of X-rays absorbed in the detector.