SiCAL, a small-angle solid-state luminosity calorimeter for ALEPH

In order to increase the precision of the luminosity measurement and to benefit from the smaller diameter of the Large Electron-Positron Collider (LEP) beam pipe, a new luminometer is being built at Scalay, in collaboration with CERN and INFN-Pisa. The design of this calorimeter, which consists of two cylinders of 12 layers each, is described. Each layer contains tungsten, used as converter, and silicon crystals, divided in pads, as the sensitive medium. The expected performances are reviewed. Special attention is given to the systematic errors. A prototype of this detector has been exposed to a 50-GeV electron beam at CERN in order to check the behaviour of the silicon detectors, front-end electronics, and full digitization and readout chain.<
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