06 01 9 v 1 5 J un 2 00 1 The JHF - Kamioka neutrino project

The JHF-Kamioka neutrino project is a second generation long base line neutrino oscillation experiment that probes physics beyond the Standard Model by high precision measurements of the neutrino masses and mixing. A high intensity narrow band neutrino beam is produced by secondary pions created by a high intensity proton synchrotron at JHF (JAERI). The neutrino energy is tuned to the oscillation maximum at ∼1 GeV for a baseline length of 295 km towards the world largest water Čerenkov detector, Super-Kamiokande. Its excellent energy resolution and particle identification enable the reconstruction of the initial neutrino energy, which is compared with the narrow band neutrino energy, through the quasi-elastic interaction. The physics goal of the first phase is an order of magnitude better precision in the νμ → ντ oscillation measurement (δ(∆m23) = 10 −4 eV2 and δ(sin 2θ23) = 0.01), a factor of 20 more sensitive search in the νμ → νe appearance (sin 2θμe ≃ 0.5 sin 2θ13 > 0.003), and a confirmation of the νμ → ντ oscillation or discovery of sterile neutrinos by detecting the neutral current events. In the second phase, an upgrade of the accelerator from 0.75 MW to 4 MW in beam power and the construction of 1 Mt Hyper-Kamiokande detector at Kamioka site are envisaged. Another order of magnitude improvement in the νμ → νe oscillation sensitivity, a sensitive search of the CP violation in the lepton sector (CP phase δ down to 10◦ − 20◦), and an order of magnitude improvement in the proton decay sensitivity is also expected.