EAPSI:Neutron Events Study of Kaon Decays for Matter-Antimatter Asymmetry in Our Universe

Su Stephanie Y, Ann Arbor MI

Investigators

Abstract

Much physics and astronomy research have been carried out to understand the early state and the development of the universe. Our current living visible world is mainly composed of matter rather than antimatter. However, the Big Bang should have created equal amounts of matter and antimatter. In the elementary physics study, charge-parity (CP) symmetry violation can explain the matter-antimatter asymmetry phenomenon. The KOTO experiment studies a rare neutral Kaon decay, which is a direct CP violating decay. The summer research will focus on the study neutron events in the experiment, which are major events that contribute to the background to identify the rare neutral Kaon decay. This research will be conducted at Osaka University, as well as at Japan Proton Accelerator Research Complex (J-PARC), in collaboration with Professor Taku Yamanaka. The Standard Model provides a clean calculation on the branching ratio of the rare neutral Kaon decay into a pion and two neutrinos. By measuring the branching ratio of this decay, we can eliminate many currently established physics models and perhaps discover new physics. Due to the missing neutrinos that cannot be detected by the detector, event signals for the rare decay will appear to have large transverse momentum. However, a neutron event generated upstream of the detector or inside the calorimeter could possibly appear to be the same. The research will use the normalization of Kaon decays with final particles to be three pions, two pions, or two photons to reconstruct the decay vertex. It will focus on the analysis on cluster information of neutron events using Monte Carlo simulation, along with known neutron events, to distinguish them from other events. Once the clustering information for the neutron events is analyzed, neural network will be trained to identify neutron events. This NSF EAPSI award is funded in collaboration with the Japan Society for the Promotion of Science.