Wan Kun ; Hiroaki Aihara

2021
University of Tokyo Tokyo

Abstract: The Belle II experiment is a next-generation super B-factory experiment. The tar- geted instantaneous luminosity is 8 × 1035 cm−2s−1 and the expected integrated lumi- nosity is 50 ab−1 by 2030 with the majority of data collected at the Υ(4S) resonance using SuperKEKB accelerator. The thesis is based on the time-dependent CP violation study of B0 → KS0KS0KS0 decay to precisely measure the CP parameters S and A in penguin-dominated b → s transition, which is sensitive to New Physics effects. Such a precise measurement mainly depends on determination of the distance between two vertices of two neutral B mesons. The blind analysis and fit by a unbinned maximum likelihood method are performed using about 62.8 fb−1 recorded experiment data from Belle II detector 2019 and 2020 (spring and summer) operation. The measurement results: S = −sin(2φ1) = −0.82±0.85 (stat)±0.07 (syst) and A = −0.21±0.28 (stat)±0.06 (syst) are obtained. The result is dominated by the statistical uncertainty and currently consistent with the Standard Model, as well as the previous results in the Belle and BaBar. At the 50 ab−1 future Belle II full luminosity, we estimate the total uncertainty of S to be 0.040 ∼ 0.048 in B0 → KS0KS0KS0. This estimation is a preliminary result based on the limited data at present and conservative assumptions on the reduction of the uncertainties, which is subject to change in future. Overall, such total uncertainty can provide a much better probe for searching the New Physics effects in future.

Note: Presented on 13 04 2021
Note: PhD