Measuring the CP-violating phase by a long base-line neutrino experiment with Hyper-Kamiokande

We study the sensitivity of a long-base-line (LBL) experiment with neutrino beams from the High Intensity Proton Accelerator (HIPA), that delivers 1021 POT per year, and a proposed 1Mt water-Čerenkov detector, Hyper-Kamiokande (HK) 295km away from the HIPA, to the CP phase (δ MNS ) of the three-flavor lepton mixing matrix. We examine a combination of the νμ narrow-band beam (NBB) at two different energies, 〈pπ〉 = 2, 3GeV, and the νμ NBB at 〈pπ〉 = 2GeV. By allocating one year each for the two νμ beams and four years for the νμ beam, we can efficiently measure the νμ → νe and νμ → νe transition probabilities, as well as the νμ and νμ survival probabilities. CP violation in the lepton sector can be established at 4σ (3σ) level if the MSW large-mixing-angle scenario of the solar-neutrino deficit is realized, |δ MNS | or |δ MNS − 180◦| > 30, and if 4|Ue3|(1− |Ue3|) ≡ sin 2θCHOOZ > 0.03 (0.01). The phase δ MNS is more difficult to constrain by this experiment if there is little CP violation, δ MNS ∼ 0 or 180, which can be distinguished at 1σ level if sin 2θ CHOOZ ∼> 0.01. PACS : 14.60.Lm, 14.60.Pq, 01.50.My