Prospects of Very Long Base-Line Neutrino Oscillation Experiments with the KEK-JAERI High Intensity Proton Accelerator

We study physics potential of Very Long Base-Line (VLBL) Neutrino-Oscillation Experiments with the High Intensity Proton Accelerator (HIPA), which will be completed by the year 2007 in Tokai-village, Japan, as a joint project of KEK and JAERI (Japan Atomic Energy Research Institute). The HIPA 50 GeV proton beam will deliver neutrino beams of a few GeV range with the intensity about two orders of magnitude higher than the present KEK beam for K2K experiment. As a sequel to the proposed HIPA-to-Super-Kamiokande experiment, we study impacts of experiments with a 100 kton-level detector and the base-line length of a few-thousand km. The pulsed narrow-band νμ beams (NBB) allow us to measure the νμ → νe transition probability and the νμ survival probability through counting experiments at large water-Čerenkov detector. We study sensitivity of such experiments to the neutrino mass hierarchy, the mass-squared differences, the three angles, and one CP phase of the three-generation lepton-flavor-mixing matrix. We find that experiments at a distance between 1,000 and 2,000 km can determine the sign of the larger mass-squared difference (m3 − m1) if the mixing between νe and ν3 (the heaviestor-lightest neutrino) is not too small; 2|Ue3|(1 − |Ue3|) ∼> 0.03. The CP phase can be constrained if the |Ue3| element is sufficiently large, 2|Ue3|(1 − |Ue3|) ∼> 0.06, and if the smaller mass-squared difference (m2−m1) and the Ue2 element are in the prefered range of the large-mixing-angle solution of the solar-neutrino deficit. The ∗e-mail:[email protected] †e-mail:[email protected] ‡e-mail:[email protected] §e-mail:[email protected] ¶e-mail:[email protected] ‖e-mail:[email protected] magunitude ∣∣m23 −m21∣∣ and the matrix element Uμ3 can be precisely measured, but we find little sensitivity to m2 −m1 and the matrix element Ue2. PACS : 14.60.Lm, 14.60.Pq, 01.50.My