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 10(21) POT per year, and a proposed 1 Mt water Cerenkov detector, Hyper-Kamiokande (HK) 295 km away from the HIPA, to the CP phase (delta(MNS)) Of the three-flavor lepton mixing matrix. We examine a combination of the v. narrow-band beam (NBB) at two different energies, [p(pi)] = 2, 3 GeV, and the (ν) over bar (mu) NBB at [p(pi)] = 2 GeV By allocating one year each for the two nu(mu) beams and four years for the (ν) over bar (mu) beam, we can efficiently measure the nu(mu) --> nu(e) and (ν) over bar (mu) --> (ν) over bar (e) transition probabilities, as well as the nu(mu) and (ν) over bar (mu) survival probabilities. CP violation in the lepton sector can be established at 4sigma (3sigma) level if the NISW large-mixing-angle scenario of the solar-neutrino deficit is realized, \delta(MNS)\ or \deltaMNS - 180degrees\ > 30degrees, and if 4\U-e3\(2)(1 - \Ue(3)\(2)) equivalent to sin(2) 2theta(RCT) > 0.03 (0.01). The phase delta(MNS) is more difficult to constrain by this experiment if there is little CP violation, delta(MNS) similar to 0degrees or 180degrees, which can be distinguished at 1sigma level if sin(2) 2theta(RCT) greater than or similar to 0.01. (C) 2003 Elsevier Science B.V. All rights reserved.