First beam loss measurements in the SuperKEKB positron ring using the fast luminosity monitor diamond sensors

SuperKEKB is a very high luminosity ${e}^{+}{e}^{\ensuremath{-}}$ collider consisting of a low energy ring (LER) of positrons of 4 GeV and a high energy ring (HER) of electrons of 7 GeV. The high luminosity will be achieved thanks to the nanobeam scheme, where very strongly focused beams (${\ensuremath{\sigma}}_{y}=60\text{ }\text{ }\mathrm{nm}$) will collide at a large crossing angle of 83 mrad. To maintain high luminosity operation, fast luminosity monitoring is essential in the presence of dynamic instabilities, for feedback and optimization. Fast luminosity monitors consisting of a single crystalline diamond sensor (LAL), a Cherenkov and scintillator detector (KEK) were placed in both rings downstream of the IP (interaction point) to measure the signal from the radiative Bhabha process at zero photon scattering angle ($\ensuremath{\sigma}\ensuremath{\approx}200\text{ }\text{ }\mathrm{mbarn}$). During single beam commissioning of SuperKEKB, the fast luminosity monitors were used as beam loss monitors to measure the single beam losses (beam-gas bremsstrahlung, Touschek scattering, Coulomb scattering). In this paper, a detailed description of the experimental setup, the data acquisition scheme, the data analysis and the comparison with the simulation for the diamond sensors, will be reported.