CRT of the Belle II iTOP detector and search for the rare decay Bs ->Ks π0 in Belle data

by Dr Tao LUO (University of Pittsburgh)

Tuesday 27 Sep 2016, 10:30 → 12:30 Asia/Shanghai

A419 (IHEP)

Abstract: The Belle II experiment is being constructed at the KEK laboratory in Japan and represents a substantial upgrade to both the Belle detector and the KEKB accelerator. An important enhancement in the upgrade of the Belle detector is the particle identification. Due to space constraints imposed on such a barrel sub-detector update, a novel 8192-channel imaging Time of Propagation (iTOP) detector is being built. In iTOP passage of hadrons through quartz panels generates Cerenkov light, which, after multiple reflections, gets collected by 16-channel micro-channel plate photomultipliers (MCP-PMTs). Every photomultiplier anode wire is inserted in an individual socket of a so-called front board, which is parallel to the MCP-PMT back surface. The signals are routed to the pads mounted on the back plane of the front board. Both position and timing information are used to identify particle species. In order to examine the status of the optics and the mirrors, the connection of bar-bar joint, and the performance of the front-end-electronic and MCP-PMT, Cosmic-ray test (CRT) is very essential. This talk will introduce the structure of the CRT test stand, the DAQ of the CRT and the iTOP performance obtained from the CRT. Performance of the more than 8k installed channels will also be presented. Two-body charmless hadronic decays of B mesons are important not only to understand the CP-violation and flavor mixing in the Standard Model (SM), but also to probe the new physics (NP) sceneries beyond the SM. In the second part of this talk, I will present the search for the rare decay process Bs-> Ks π0 in Belle data. In the SM, this process proceeds mainly via a b->d “penguin” diagram, and it has not been observed yet; there is no record of measurement in PDG. Belle is more sensitive to this decay than LHCb because of the neutral particles in the final states. Discrepancy of measured branching fractions from the theoretical calculation for this channel will indicate BSM physics. An important feature of this analysis is that we are using so-called Neural Network (NN) to select Ks candidates and to suppress the huge continuum background. This method can increase the signal selection efficiency greatly.