The operation and performance of the TOP detector at the Belle II experiment

Abstract

TheSuperKEKB/Belle II experiment, the successor of theKEKB/Belle experiment atKEK, started the physics data taking with the full detector system in March 2019. The Time-of-Propagation (TOP) detector was integrated into the Belle II detector for charged particle identification in the barrel region. The TOP detector mainly consists of quartz radiators, Micro-Channel-Plate (MCP) PMTs, and front-end electronics. It reconstructs a ring image of Cherenkov photons generated by an incident particle. It measures the timing of each detected photon with an accuracy of less than 100 ps for good /c separation. In the operation of the TOP detector, harsh beam-induced background in the high luminosity environment is one of the critical issues to keep the particle identification performance. We developed various tools to monitor MCP-PMT performance and to identify and fix errors arising from front-end electronics during data taking. The TOP detector provides 85% identification efficiency at a 10% c misidentification rate in the data at the early stage of the experiment. In these proceedings, we present the operation status and the performance by the summer of 2021.