The small angle electromagnetic calorimeter at SLD: a 2m 2 application of silicon detector diodes

The SLD (Stanford Linear Collider Large Detector) collaboration is preparing a solenoidal detector at SLAC (Stanford Linear Accelerator Center) to measure the properties of Z⁰ decays at the SLC (Stanford Linear Collider). One feature of this detector is the nearly 4π coverage of the electromagnetic calorimetry extending down to 23 mrad from the beam axis. The smallest angle coverage (23-200 mrad) is provided by calorimeters using silicon detector readout. These calorimeters are twenty-three radiation lengths in depth, segmented longitudinally every radiation length, and the twenty-three layers of silicon detectors are ganged into towers of roughly 1-2-cm² cross section. These towers are read out as two signals, one from the first six radiation lengths and one from the last seventeen. The design and construction of these devices is presented. The potential of the approach for silicon hadron calorimeters at future colliders is also discussed