Nakagiri, Kota. Search for the Decay K_L → π^0 u\bar at the J-PARC KOTO Experiment [electronic resource] / / by Kota Nakagiri.. — 1st ed. 2020.. — XVI, 151 p. 121 illus., 109 illus. in color. : online resource. — (Springer Theses, Recognizing Outstanding Ph.D. Research,) 2190-5053. - Springer Theses, Recognizing Outstanding Ph.D. Research, .
Introduction -- The KOTO Experiment -- Data Taking -- Event Reconstruction -- Monte Carlo Simulation -- Analysis of the KL →π0νν and KL →π0X0 Searches -- Discussion -- Conclusion -- Appendix.
Анотація: This book reports on a new result from the KL→π0νν search at the J-PARC KOTO experiment, which sets an upper limit of 3×10-9 for the branching fraction of the decay at the 90% confidence level, improving the previous best limit by an order of magnitude. To explain the matter–antimatter asymmetry in the universe, still unknown new physics beyond the standard model (SM) that breaks CP symmetry is necessary. The rare decay of a long-lived neutral K meson, KL→π0νν, is a CP-violating decay. It is an excellent probe to search for new physics because new physics can contribute to the decay and change its branching fraction, while the SM is as small as 3×10-11. However, it is extremely difficult to search for because all of the decay products are neutral and two neutrinos are undetectable. The KL→π0νν signal is identified by measuring two photons from a π0 with a calorimeter and confirming the absence of any other detectable particles with hermetic veto counters. The book contributes to the analysis of neutron-induced backgrounds which were the dominant background sources in the search. For the background caused by two consecutive hadronic showers in the calorimeter due to a neutron, the author evaluated the background yield using a data-driven approach. For another background caused by an η meson production—η decays two photons—by a neutron that hits a veto counter near the calorimeter, the author developed an original analysis technique to reduce it. The book also contributes to the analysis of the normalization modes (KL→3π0, KL→2π0, KL→2γ) to measure KL yield, the estimation of the signal acceptance based on a simulation, and the evaluation of the trigger efficiency. As a result, significant improvements in the measurement were achieved, and this is an important step in the continuing higher sensitivity search, which can reach new physics with the energy scales up to O(100-1000 TeV).
9789811564222
10.1007/978-981-15-6422-2 doi
Nuclear physics. Heavy ions. Particle acceleration. Elementary particles (Physics). Quantum field theory. Nuclear Physics, Heavy Ions, Hadrons. Particle Acceleration and Detection, Beam Physics. Elementary Particles, Quantum Field Theory.