New Developments of Accelerator Neutrino Experiments

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In this research, we have (1) conducted the world first long baseline neutrino oscillation (LBNO) experiment, K2K, with a baseline distance of 250 km between KEK and Kamioka ; (2) made planning of a next generation LBNO experiment utilizing the JHF high intensity proton synchrotron under construction at Tokai ; and (3) made a feasibility study of a neutrino factory, future high-intensity neutrino source, in Japan.Concerning item (1), we have reported the data corresponding to the integrated beam intensity of about half of our goal (defined as 10^<20> protons delivered onto the production target). The results are consistent with ν_μ→ν_τ oscillation discovered by the Super-Kamiokande Collaboration through observations of atmospheric neutrinos. The probability that statistical fluctuations fake these results is less than 1 %. The K2K experiment will reach the goal by the end of March, 2005.Concerning item (2), we have prepared an LOI (letter of intent) of the next generation LBNO experiment from Tokai to Kamioka with a distance of 295 km. The LOI was signed by about 150 physicists from 12countries, and wassubmitted by this international team to the JHF headquarters. A sort of pre-Program Advisory Committee reviewed this LOI and recommended early realization of the experiment, recognizing its very high priority.Concerning item (3), we have proposed a unique Japanese scheme for a neutrino factory, based on FFAG (Fixed-Field Altenating Gradient) accelerators and a muon storage ring. This scherme attracted worldwide interests. We have presented a detailed study report, and currently an R&D of 150 MeV FFAG is underway. We have also submitted an LOI to the JHF headquarters, proposing the utilization of the JHF high-intensity proton synchrotron as a future muon source to realize this idea of the FFAG-based neutrino factory.