A precision luminometer for future linear collider experiments

The FCAL collaboration develops the technologies of compact and fast calorimeters to measure the luminosity at Linear Collider experiments both with high precision using small angle Bhabha scattering, and bunch-by-bunch using beamstrahlung pairs. Beside the luminosity measurement, the capability of detecting high energy electrons at low angles is important for many search experiments. A small Molière radius facilitates the measurement of Bhabha events in the presence of background and allows the detection of single high energy electrons on top of the widely spread background of beamstrahlung. A multi-plane prototype of a compact precision luminometer was studied in an electron beam with energies between 1 and 5 GeV at DESY. The results for the longitudinal and the transverse shower profiles are compared with Geant4 simulations of the setup. Very good agreement was obtained. The effective Molière radius of the prototype was determined. Again, very good agreement between data and Monte Carlo simulations was found. The value of the Molière radius approached the technological limit. A dedicated multi-channel ultra-low power readout ASIC is under development in 130 nm CMOS, comprising an analogue front-end and fast 10-bit ADC in each channel, followed by fast serialization and data transmission. In addition, an ASIC with a dual readout scheme allowing for a fast feedback to the accelerator and simultaneous data taking and calibration is under development. The paper summarizes the results on design optimization, beam-tests and the status of the readout ASICs