Time of Flight resolution of the prototype of the electromagnetic calorimeter PHOS

The Time of Flight (TOF) resolution of one of the LHC ALICE detectors, a prototype of the electromagnetic calorimeter PHOS (PHOton Spectrometer), was measured in beam tests carried out at CERN PS. The prototype of the calorimeter consists of 256 (22×22×180mm3) cells of light-detecting PbWO4 (PWO) monocrystals read out with 5×5mm2 Avalanche Photo Diodes (APDs). Three dedicated front end cards with 24 channels of electronics were designed and produced for using in the tests, each channel consisting of one fast and two slow shapers, a time to amplitude converter and three identical 12-bit peak sensitive Analog to Digital Converters (ADCs). The high voltage bias regulator for APD is located on the same card. The measured TOF resolution is described as σt=0.24/EGeV2+0.4ns.