The PHOBOS silicon pad sensors

PHOBOS is one of the four experiments at the Relativistic Heavy Ion Collide r at Brookhaven National Laboratory. PHOBOS utilizes silicon sensors to mea sure charged particle multiplicity distributions and to track particles in a 2-arm spectrometer. The detector consists of 450 silicon pad sensors. Nin e different pad geometries are used to match the different physics needs of the experiment. A relatively high granularity, of up to 1536 channels per sensor, is used in the spectrometer. The multiplicity detector uses 128 and 64 channel sensors and the charge deposition per pad is measured to determ ine the multiplicity of single events. All sensors are of the double-metal silicon pad type with pad sizes from 1 up to 4 cm(2). They are produced in Taiwan by the ERSO foundry under supervision of Miracle Co. and National Ce ntral University. An extensive testing procedure makes it possible to selec t sensors suited for use in PHOBOS, Detector modules consisting of up to 5 sensors are read out with integrated chips of either 64 or 128 channels. Th e test results of the sensors and the performance of the assembled detector modules are discussed. (C) 2000 Elsevier Science B.V, All rights reserved.