XXth International Conference on Neutrino Physics and Astrophysics
N.Okamura
Measuring the CP-Violating Phase by a Long Baseline
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 10^22 POT per year and a proposed 1 Mt water-Cherenkov
detector, Hyper-Kamiokande (HK), to the CP phase (delta_mns) of the
three-flavor lepton mixing matrix. We examine a combination of the
nu_mu narrow-band beam (NBB) at two different energies, vev{p_pi} = 2,
3 GeV, and the anti-nu_mu NBB at vev{p_pi} = 2 GeV. By allocating one
year each for the two nu_mu beams and four years for the anti-nu_mu
beam, we can efficiently measure the nu_mu -> nu_e and anti-nu_mu ->
anti-nu_e transition probabilities, as well as the nu_mu and
anti-nu_mu survival probabilities. CP violation in the lepton sector
can be established at 3 sigma level if the MSW large-mixing-angle
scenario of the solar-neutrino deficit is realized, delta_mns ~ 90^o
or 270^o, and if 2|Ue3|^2 (1-|Ue3|^2) = sin^2(2 theta_chooz) > 0.01.
The delta_mns is more difficult to constrain by this experiment if
there is little CP violation, delta_mns ~ 0^o or 180^o; it is
constrained at 1 sigma (2 sigma) level if sin^2(2theta_chooz) >~ 0.01
(>~ 0.06).
Based on a paper in preparation.