Shoei Nakayama

Resolving the eightfold neutrino parameter degeneracy by two identical detectors with different baselines

We have shown in a previous paper that two identical detectors with each fiducial mass of 0.27 megaton water, one in Kamioka and the other in Korea, which receive the (anti-) muon neutrino beam of 4 MW power from J-PARC facility have potential of determining the neutrino mass hierarchy and discovering CP violation by resolving the degeneracies associated with them. In this paper, we point out that the same setting has capability of resolving the {theta}{sub 23} octant degeneracy in region where sin{sup 2}2{theta}{sub 23} < or approx. 0.97 at 2 standard deviation confidence level even for very small values of {theta}{sub 13}. Altogether, it is demonstrated that one can solve all the eightfold neutrino parameter degeneracies in situ by using the Tokai-to-Kamioka-Korea setting if {theta}{sub 13} is within reach by the next generation superbeam experiments. We also prove the property called decoupling between the degeneracies, which is valid to first-order in perturbation theory of the earth matter effect, that guarantees approximate independence between analyses to solve any one of the three different type of degeneracies.

Probing Nonstandard Neutrino Physics by Two Identical Detectors with Different Baselines

The Kamioka-Korea two-detector system is a powerful experimental setup for resolving neutrino parameter degeneracies and probing CP violation in neutrino oscillation. In this paper, we study sensitivities of the same setup to several nonstandard neutrino physics such as quantum decoherence, tiny violation of Lorentz symmetry, and nonstandard interactions of neutrinos with matter. We show that it can achieve significant improvement on the current bounds on nonstandard neutrino physics. In most cases, the Kamioka-Korea two-detector setup is more sensitive than the one-detector setup, either in Kamioka or in Korea, except for the cases when Lorentz symmetry is broken in a CPT-violating manner and the nonstandard neutrino interactions with matter is present.

T2K: New physics results

The T2K experiment is designed to probe the θ13 neutrino mixing parameter by looking for the appearance of νe in a pure νμ beam and to precisely measure atmospheric Δm2 and θ23 parameters. A neutrino beam produced at J-PARC, Japan, is aimed at 2.5° off-axis angle to the Super-Kamiokande far neutrino detector, 295km away. The narrow energy neutrino beam peaked at about 600 MeV is optimized to maximize the probability of oscillation at the atmospheric Δm2 scale. The neutrino beam is monitored by a complex of neutrino near detectors at 280m from the production target. T2K has successfully operated since January 2010. Data-taking has been presently paused due to the recent earthquake in Japan. Results on measurements of νe appearance and νμ disappearance are reported.

A Test of New Large Aperture Photodetectors in a Water Cherenkov Detector

Yuji OKAJIMAa, Miao JIANGb, Daisuke FUKUDAc, Ryosuke AKUTSU, Yusuke SUDAd, Seiko HIROTAb, Shoei NAKAYAMAe, Masato SHIOZAWAe, Masashi YOKOYAMAd, Yoshinari HAYATOe, Hidekazu TANAKAe, Masayuki NAKAHATAe, Tsuyoshi NAKAYAb, Masahiro KUZEa, Yusuke KOSHIOc, Akimichi TAKETA f aDepartment of Physics, Tokyo Institute of Technology bDepartment of Physics, Kyoto University cDepartment of Physics, Okayama University dDepartment of Physics, The University of Tokyo eKamioka Observatory, Institute for Cosmic Ray Research, The University of Tokyo f Earthquake Research Institute, The University of Tokyo

Detailed performance evaluation of a new 20-inch photomultiplier tube with a Box and Line dynode

Yasuhiro Nishimuraa, Ryosuke Akutsua, Yusuke Sudab, Miao Jiangc, Seiko Hirotac, Daisuke Fukudad , Masahiro Kuzee, Masaki Ishitsukae, Masayuki Nakahataa, Masato Shiozawaa, Yoshinari Hayatoa, Shoei Nakayamaa, Hidekazu Tanakaa, Masashi Yokoyamab, Tsuyoshi Nakayac, Akihiro Minaminoc, Akimichi Taketa f , Yoshihiko Kawaig, Takayuki Ohmurag, Masatoshi Suzukig a Institute for Cosmic Ray Research, University of Tokyo b Department of Physics, University of Tokyo c Department of Physics, Kyoto University d Department of Physics, Okayama University e Department of Physics, Tokyo Institute of Technology f Earthquake Research Institute, University of Tokyo g Hamamatsu Photonics K.K.

Temperature Dependence Measurement of a Hybrid Photo-Detector for Hyper-Kamiokande

1 Department of Physics, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan 2 Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan 3 Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan 4 Department of Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan 5 Earthquake Research Institute, University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan 6 Hamamatsu Photonics K.K., Hamamatsu, Shizuoka, 430-8587, Japan

Development and measurement of new large-aperture photodetectors for Hyper-Kamiokande

Two types of new photodetectors are currently being developed with a large aperture, for use in the large water Cherenkov detector, Hyper-Kamiokande planned in Japan [1]: Hybrid Photo-Detector (HPD) of a 20-inch diameter size with an avalanche diode and a 20-inch Photomultiplier Tube (PMT) with a dynode upgrade to a box-and-line type. These are expected to have an excellent performance about timing and collection efficiency compared to a 20-inch PMT with a venetian blind dynode used in Super-Kamiokande. Also there is a possibility to improve quantum efficiency (QE) of these photodetectors from 22% to around 30% using the super-bialkali technique. A proof test in a smaller water Cherenkov detector is planned in advance for these photodetectors to determine the best candidate for Hyper-Kamiokande. Two prototypes of new photodetectors have already been manufactured for testing: the 8-inch HPD, and a 20-inch PMT with a higher QE of 30% compared with 22% of the 20-inch PMT used in Super-Kamiokande. These photodetectors were installed in a 200-ton water tank in summer 2013 for a proof of using test in a water Cherenkov detector. We report the specification of these photodetectors, a status and plan of the development and proof test.

NON-STANDARD NEUTRINO PHYSICS PROBED BY TOKAI-TO-KAMIOKA-KOREA TWO-DETECTOR COMPLEX

The discovery potentials of non-standard physics (NSP) which might be possessed by neutrinos are examined by taking a concrete setting of Tokai-to-Kamioka-Korea (T2KK) two detector complex which receives neutrino superbeam from J-PARC. We restrict ourselves into nu_{mu} and bar{nu}_{mu} disappearance measurement. We describe here only the non-standard interactions (NSI) of neutrinos with matter and the quantum decoherence. It is shown in some favorable cases T2KK can significantly improve the current bounds on NSP. For NSI, for example, epsilon_{mutau} < 0.03, which is a factor 5 severer than the current one.