CLAWS — a plastic scintillator / SiPM based detector to measure backgrounds at SuperKEKB

The SuperKEKB collider at KEK, which has started its commissioning with beam in February 2016, is designed to achieve unprecedented luminosities, with a factor 40 higher than the record-breaking luminosity of the KEKB machine. For the operation of the Belle II detector, in particular of its pixel vertex detector, a precise understanding of the background conditions at the interaction point of the accelerator is crucial. To study these conditions prior to the final installation of the Belle II experiment, a dedicated detector setup consisting of different subsystems has been installed for the first commissioning phase of the accelerator. Among those systems is sCintillation Light And Waveform Sensors (CLAWS), consisting of eight plastic scintillator tiles with directly coupled silicon photomultipliers (SiPMs). These detectors are read out with computer-controlled oscilloscopes with very deep buffers to enable the continuous measurements of charged particles close to the Belle II interaction point over millisecond time frames. This contribution discusses the technical details of the CLAWS setup, the calibration with cosmic muons in the laboratory including the determination of the time resolution, the effect of radiation during the first SuperKEKB commissioning phase and presents a first validation of the performance with beam in the accelerator.