High Energy K L Calibration at Belle II using Initial State Radiation

Abstract

This thesis presents a feasibility study of a method for KL calibration at the Belle II experiment, using initial state radiation (ISR) production of the KS KL final state. By reconstructing the ISR photon, and the KS and subtracting their energy-momentum 4-vectors from that of the known e+ e − initial state, the 4-vector of the KL may be determined. Due to the loss of second order ISR photons and lost photon energy from incomplete electromagnetic shower reconstruction, a correction is applied to the photon energy. The expected efficiency, after all of the appropriate selections to isolate signal events were applied, was found to be of order 1%. This corresponds to roughly 100 well-reconstructed events per f b −1 of integrated luminosity produced at Belle II, with the difference between the MC generated and reconstructed KL energy found to be of the order of 5 MeV and with the angle between the truth and determined K L vector found to be of the order 0.02 radians=1.1◦. At this production rate, the currently available early Belle II data, which have an integrated luminosity of only 472pb−1, are likely not large enough for a meaningful KL calibration, however, Belle II is expected to produce 50ab−1 of integrated luminosity. As Belle II produces more data this method will become more and more feasible.