The small angle electromagnetic calorimeter at sld: A 2m2 application of silicon detector diodes

The SLD Collaboration is preparing a solenoidal detector at SLAC to measure the properties of Z0decays at SLC. One feature of this detector is the nearly 4π coverage of the electromagnetic calorimetry, extending down to 23 milliradians from the beam axis. The smallest angle coverage (23–200 milliradians) is provided by calorimeters employing 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 square centimeters 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 for silicon hadron calorimeters at future colliders is also discussed.