The forward region of the future ILC detector

In the very forward region of the future detector at the International Linear Collider (ILC) the following subsystems will be considered: a luminosity detector (LumiCal) for precise measurement of the Bhabha event rate; a beam calorimeter (BeamCal) and a beamstrahlung photon monitor (GamCal) for providing a fast feed-back in tuning the luminosity. BeamCal and GamCal will support also the determination of beam parameters. Both LumiCal and BeamCal will extend the angular coverage of the electromagnetic calorimeter at small polar angles. Detailed simulations are currently done to optimize the design of these detectors. Both LumiCal and BeamCal are planned as compact and highly segmented sandwich calorimeters. Tungsten disks of one X0 thickness are interspersed with sensor planes. For LumiCal, silicon pad sensors will be used. BeamCal will work in an extreme radiation environment, hence radiation hard sensors will be used. The sensors have to withstand a dose of up to several MGy per year. Several options for possible sensor materials have been investigated: polycrystalline and single crystal CVD diamond, as well as GaAs. Since the occupancy of LumiCal is relatively large and BeamCal must be readout after each bunch crossing, a fast readout electronics is necessary. The uncertainty of the luminosity measurement must be smaller than 10−3 for the running at high energy and about 10−4 in the GigaZ program focused to precision measurements of the Z boson. Systematic effects originating from hardware design as the accuracy of the sensor position, the calorimeter position and the dynamic range of the readout electronics, but also from physics processes have been studied. This work presents the current status of the research carried out to instrument this difficult region of the future ILC detector.