A new electronic readout
for CsI-coated multiwire proportional chambers (MWPC), used as photon detectors in the COMPASS ring imaging Cherenkov (RICH) detector, is described. A prototype system comprising more than 5000 channels has been built and tested in high-intensity beam conditions. It is based on the APV25-S1 analogue sampling chip, and replaces the GASSIPLEX chip readout used previously. The APV25 chip, although originally designed
for Silicon microstrip detectors, is shown to per
form well even with “slow” signals
from an MWPC, maintaining a signal-to-noise ratio (SNR) o
f 9. For every trigger the system reads out three consecutive amplitudes in time, thus allowing to extract in
formation on both the signal amplitude and its timing. This in
formation is used to reduce pile-up events in a high-rate environment. Prototype tests o
f the new readout electronics on a central RICH photocathode in nominal COMPASS beam conditions showed that the e
ffective time window is reduced
from more than
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for the GASSIPLEX to less than
f="/science?_ob=MathURL&_method=retrieve&_udi=B6TJM-4S08JRR-B&_mathId=mml7&_user=1067359&_cdi=5314&_rdoc=4&_acct=C000050221&_version=1&_userid=10&md5=79797e5385dcdd6d07aa455a420e043a">
for the APV25 chip. This leads to a signi
ficant improvement o
f the signal-to-background ratio (SBR) with respect to the original readout. A gain by a
factor o
f 5–6 was experimentally veri
fied in the very
forward region o
f phase space, where pile-up due to the muon beam halo is most signi
ficant. Owing to its pipelined architecture, the new readout system also considerably reduces the dead time per event, thus allowing to make use o
f trigger rates exceeding
f="/science?_ob=MathURL&_method=retrieve&_udi=B6TJM-4S08JRR-B&_mathId=mml8&_user=1067359&_cdi=5314&_rdoc=4&_acct=C000050221&_version=1&_userid=10&md5=6a192554a58995e32e6b87afed4f1eec">![View the MathML source View the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6TJM-4S08JRR-B-39/0?wchp=dGLbVtb-zSkWz)
.