A fast luminosity monitor based on diamond detectors for the SuperKEKB collider

A fast luminosity monitor measuring the rate of the radiative Bhabha process at zero degree photon scattering angle based on diamond detectors was developed and successfully operated during the Phase-2 commissioning of SuperKEKB. The main purpose of this system, called LumiBelle2, is to provide: train integrated luminosity signals at 1 kHz with a relative precision better than 1% for luminosities higher than 1034 cm−2s−1, input to a dithering feedback system designed to maintain an optimum horizontal overlap between the two colliding beams at the Interaction Point (IP), and bunch integrated luminosity signals at 1 Hz which are useful for machine tuning and beam parameters studies of the successive bunches along the train. In this paper, the design of the LumiBelle2 and Phase-2 results will be reported, including the evaluation of the single beam background, relative luminosity measurements and vertical beam size determinations at the IP using vertical offset scans.