Instrumentation of the very forward region of a linear collider detector

Calorimeters in the very forward region of the ILC detector are necessary to extend the coverage to small polar angles, to measure the luminosity delivered by the accelerator and to assist the beam tuning. A silicon-tungsten calorimeter, LumiCal, is planned to measure the luminosity. It will be placed at relatively large polar angles where background from beamstrahlung is negligible. Calorimeters at smaller polar angles, denoted as BeamCal and PhotoCal, are hit by a large amount of beamstrahlung, hence radiation hard sensors are needed. BeamCal will extend the detector coverage for high energy electron detection down to about 5 mrad. BeamCal and PhotoCal will serve for tuning the beam to maximum luminosity. Monte Carlo simulations to optimize the design are performed. Technological options for the innermost calorimeters are discussed. (orig.)