New Views on the Problem of CP Violation

Abstract

After briefly recollecting basic features of the good-old way of detecting CP violation by comparing nu_{e} and nu_{e}-bar appearance measurement in long-baseline (LBL) neutrino oscillation experiments, I discuss two new ways of exploring leptonic CP violation. First, I discuss the reactor-LBL method in which reactor measurement of theta_{13} is combined with nu_{e} (no nu_{e}-bar) appearance measurement in LBL.. Assuming \sim 10^{3} GW_{th} ton year operation of a reactor experiment, CP sensitivity at 90 % CL is shown to exists in sin^2{2theta_{13}} > 0.03 (0.04) with 2 years running of Hyper-Kamiokande (10 years running of SK). Second, I review the method which I call the BNL strategy, in which one tries to explore CP violation through observing oscillatory pattern of neutrino oscillation. Motivated by the approval of the JPARC neutrino program, I also discuss a low-energy realization of the BNL strategy. It is meant to measure neutrino oscillation at the first and the second oscillation maxima by two HKs placed at Kamioka and somewhere in Korea. It is suggested by very rough argument that 8 years running in nu_{e} and nu_{e}-bar modes with one HK at Kamioka is equivalent to 2 years running in nu_{e} mode with two HK complex.