Prof. Yasuyuki Horii
The Belle II experiment is an upcoming experiment based on the SuperKEKB e+e- collider, which will provide almost two orders of magnitude higher instantaneous luminosity than the KEKB e+e- collider. We aim to measure precisely the parameters of the Standard Model and search for physics beyond the Standard Model. We report here on the time-of-propagation (``TOP'') detector, which plays an essential role in the identification of charged particles at the Belle II experiment. Each TOP counter consists of a quartz radiator and 32 micro-channel-plate photomultiplier tubes (``MCP-PMTs''). The Cherenkov photons traveling in the quartz radiator are detected by the MCP-PMTs, and the time and the position are used to reconstruct the Cherenkov angle corresponding to the velocity. The quartz radiator is polished with a roughness of < 0.5 nm in RMS and a flatness of < 6.3 um to ensure photon efficiency and maintain the angles of the Cherenkov photons, respectively, over hundreds of reflections at the quartz surfaces. The MCP-PMTs can detect single photons with a timing resolution better than 50 psec. The key features of the TOP counter as well as a performance study using a full-size prototype are presented. We plan to install 16 TOP counters in the Belle II detector in early 2015. The status and the plan for the construction are also shown.
Yasuyuki Horii (Nagoya University)