The electronics of the H1 lead/scintillating-fibre calorimeters

The electronic system developed for the SpaCal lead/scintillating-fibre cal orimeters of the I-Il detector in operation at the HERA ep collider is desc ribed in detail and the performance achieved during H1 data taking is prese nted. The 10 MHz bunch crossing rate of HERA puts severe constraints on the requirements of the electronics. The energy and time readout are performed , respectively, with a 14-bit dynamic range and with a resolution of simila r to 0.4 ns. The trigger branch consists of a nanosecond-resolution calorim etric time of flight for background rejection and an electron trigger based on analog 'sliding windows'. The on-line background rejection currently ac hieved is similar to 10(6). The electron trigger allows a low-energy trigge r threshold to be set at similar to 0.50 +/- 0.08 (RMS) GeV with an efficie ncy greater than or equal to 99.9%. The energy and time performance of the readout and trigger electronics is based on a newly developed low noise (si gma(noise) similar to 0.4 MeV) wideband (f less than or equal to 200 mHz) p reamplifier located at the output of the photomultipliers which are used fo r the fibre light readout in the similar to 1 T magnetic field of H1. (C) 1 999 Elsevier Science B.V. All rights reserved.