The barrel-region particle identification detector is crucial for extending the physics reach of the Belle II experiment operating at the SuperKEKB accelerator. For this purpose, an imaging-Time-of-Propagation (iTOP) counter was developed, which is a new type of ring-imaging Cherenkov detector. The iTOP consists of 16 separate modules arranged azimuthally around the beam line. Each module consists of optical components fabricated from quartz (one mirror, one prism,  and two bars), an array of micro-channel-plate photo-multiplier tubes (MCP-PMTs), and front-end electronics.  The detector construction was completed and the detector installed by the summer of 2016, and since then the detector has undergone commissioning. This talk describes the construction and commissioning of the Belle II iTOP counter.

The decay of Bs -> Ds X is important to determine the Bs production rate at the Y(5S) resonance. The current PDG value is obtained with indirect measurements and has quite large error. By using the full Belle Y(5S) data, it’s possible to measure the branching fraction of this decay directly by using the Bs semi-leptonic tagging method to increase the statistics. This talk presents the analysis and preliminary result of the measurement.

                                               Host: Prof. Jianglai Liu