Design of a novel cherenkov detector system for machine induced background monitoring in the CMS cavern

A novel detector system has been designed for an efficient online measurement of the machine-induced background in the CMS experimental cavern. The suppression of the CMS cavern background originating from pp collision products and the 25 ns bunch spacing have set the requirements for the detector design. Each detector unit will be a radiation hard, cylindrical Cherenkov radiator optically coupled to an ultra-fast UV-sensitive photomultiplier tube, providing a prompt, directionally sensitive measurement. Simulation and test beam measurements have shown the achievability of the goals that have driven the baseline design. The system will consist of 20 azimuthally distributed detectors per end, installed at a radius of r ∼ 180 cm and a distance 20.6 m away from the CMS interaction region. The detector units will enable a measurement of the transverse distribution of the bunch-by-bunch machine induced background flux. This will provide important feedback from the CMS on the beam conditions during the LHC machine setup and comparisons to expectations based on FLUKA simulations.