New Developments of Accelerator Neutrino Experiments

在本研究中，我们进行了世界上第一个长基线中微子振荡（LBNO）实验，K2K， KEK和神冈之间的基线距离为250 km；(2)利用东海正在建设的JHF高强度质子同步加速器对下一代LBNO实验进行规划；(3)对日本未来高强度中微子源中微子工厂进行了可行性研究。关于项目(1)，我们已经报告了大约一半目标（定义为10^<20>个质子传递到生产目标）的集成光束强度对应的数据。结果与超级神冈合作小组通过观测大气中微子发现的ν_μ→ν_τ振荡一致。统计波动导致这些结果的概率小于1%。K2K实验将于2005年3月底达到目标。关于第(2)项，我们准备了从东海到神冈295公里的下一代LBNO实验的意向书（LOI）。意向书由来自12个国家的约150名物理学家签署，并由这个国际团队提交给JHF总部。一个项目前咨询委员会审查了这份意向书，并建议尽早实现这个实验，认识到它的高度优先性。关于第(3)项，我们提出了一个独特的日本中微子工厂方案，基于FFAG（固定场交替梯度）加速器和介子存储环。这个计划引起了全世界的兴趣。我们已经提交了详细的研究报告，目前正在进行150mev FFAG的研发。我们还向JHF总部提交了一份意向书，建议利用JHF高强度质子同步加速器作为未来的μ子源，以实现基于ffag的中微子工厂的这一想法。

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.