NISHIMURA Yasuhiro

写真a

Affiliation

Faculty of Science and Technology, Department of Physics 理工学部物理学科 (Yagami)

Position

Associate Professor

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Papers 【 Display / hide 】

  • Impact of external radiation on dark rate noise measurement for the Hyper-Kamiokande photomultiplier tube

    Mandokoro Y., Bronner C., Ishitsuka M., Tashiro T., Nishimura Y.

    Journal of Instrumentation 20 ( 5 )  2025.05

    　View Summary

    The Hyper-Kamiokande (HK) is a next-generation water Cherenkov detector currently under construction in Japan as of 2025, and scheduled to begin operation in 2027. A new PMT has been developed for HK with improvements in detection efficiency, timing resolution, and pressure tolerance by a factor of two with respect to those used in the Super-Kamiokande detector. The HK detector will be instrumented with 20,000 photomultiplier tubes (PMT). Currently, the PMTs are produced, and the performance testing of the delivered PMTs is underway in parallel. In this test, it was observed that the dark rate values differed depending on the measurement location. The difference is considered due to environmental radiation, and we have conducted measurements of dark rate variations with radiation sources. We measured correlations between the irradiation of γ rays and dark noise rate and the evaluated intrinsic dark noise rate of HK PMT after subtracting the contribution due to environmental radiation.

  • Optimization of geomagnetic shielding based on detection efficiency

    Cabo S.R., Nishimura Y., Gómez S.L.S., Bonavera L., Sanchez M.L., Santos J.D., de Cos F.J.

    European Physical Journal Plus 140 ( 4 )  2025.04

    　View Summary

    Due to the progressive increase in size of the latest Cherenkov-type detectors, it is becoming increasingly important to design a suitable compensation system based on coils of the Earth’s magnetic field to ensure the correct operation of the photomultipliers (PMTs). Until now, most studies have assessed the correct functioning of such a system by the proportion of PMTs experiencing more than 100 mG of magnetic field perpendicular to their axis. In the present study, we discuss whether this evaluation parameter is the most appropriate and propose the average residual perpendicular magnetic field <Bperp> as an alternative that more closely reflects the loss of detection efficiency of PMTs. A compensation system design is also proposed that offers good results as well as being economical to optimize this parameter.

  • First Joint Oscillation Analysis of Super-Kamiokande Atmospheric and T2K Accelerator Neutrino Data

    Abe K., Abe S., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakahata M., Nakano Y., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Mirabito J., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Jang M.C., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Rogly R., Nakamura T., Jang J.S., MacHado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Uchida Y., Berardi V., Calabria N.F., Catanesi M.G., Radicioni E., Langella A., De Rosa G., Collazuol G., Feltre M., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Périssé L., Pronost G., Fujisawa C., Horiuchi S., Kobayashi M.

    Physical Review Letters 134 ( 1 )  2025.01

    ISSN  00319007

    　View Summary

    The Super-Kamiokande and T2K Collaborations present a joint measurement of neutrino oscillation parameters from their atmospheric and beam neutrino data. It uses a common interaction model for events overlapping in neutrino energy and correlated detector systematic uncertainties between the two datasets, which are found to be compatible. Using 3244.4 days of atmospheric data and a beam exposure of 19.7(16.3)×1020 protons on target in (anti)neutrino mode, the analysis finds a 1.9σ exclusion of CP conservation (defined as JCP=0) and a 1.2σ exclusion of the inverted mass ordering.

  • Search for proton decay via p →e+η and p →μ+η with a 0.37 Mton-year exposure of Super-Kamiokande

    Taniuchi N., Abe K., Abe S., Asaoka Y., Bronner C., Harada M., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakahata M., Nakayama S., Noguchi Y., Pronost G., Okamoto K., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Megias G.D., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Mirabito J., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Jang M.C., Kim J.Y., Lee S.H., Lim I.T., Moon D.H., Park R.G., Yang B.S., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Bernard L., Coffani A., Drapier O., El Hedri S., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Rogly R., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Calabria N.F., Catanesi M.G.

    Physical Review D 110 ( 11 )  2024.12

    ISSN  24700010

    　View Summary

    A search for proton decay into e+/μ+ and a η meson has been performed using data from a 0.373 Mton·year exposure (6050.3 live days) of Super-Kamiokande. Compared to previous searches this work introduces an improved model of the intranuclear η interaction cross section, resulting in a factor of 2 reduction in uncertainties from this source and ∼10% increase in signal efficiency. No significant data excess was found above the expected number of atmospheric neutrino background events resulting in no indication of proton decay into either mode. Lower limits on the proton partial lifetime of 1.4×1034 years for p→e+η and 7.3×1033 years for p→μ+η at the 90% CL were set. These limits are around 1.5 times longer than our previous study and are the most stringent to date.

  • Measurements of the charge ratio and polarization of cosmic-ray muons with the Super-Kamiokande detector

    Kitagawa H., Tada T., Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakahata M., Nakano Y., Nakayama S., Noguchi Y., Okamoto K., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Megias G.D., Fernandez P., Labarga L., Ospina N., Zaldivar B., Kearns E., Raaf J.L., Wan L., Wester T., Pointon B.W., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Jang M.C., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Paganini P., Quilain B., Rogly R., Santos A.D., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Marin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Calabria N.F., Catanesi M.G., Radicioni E., Langella A., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Mattiazzi M., Ludovici L.

    Physical Review D 110 ( 8 )  2024.10

    ISSN  24700010

    　View Summary

    We present the results of the charge ratio (R) and polarization (P0μ) measurements using decay electron events collected between September 2008 and June 2022 with the Super-Kamiokande detector. Because of its underground location and long operation, we are able to perform high-precision measurements by accumulating cosmic-ray muons. We measured the muon charge ratio to be R=1.32±0.02(stat+syst) at EμcosθZenith=0.7-0.2+0.3 TeV, where Eμ is the muon energy and θZenith is the zenith angle of incoming cosmic-ray muons. This result is consistent with the Honda flux model while indicating a tension with the πK model of 1.9σ. We also measured the muon polarization at the production location to be P0μ=0.52±0.02 (stat+syst) at the muon momentum of 0.9-0.1+0.6 TeV/c at the surface of the mountain; this also suggests a tension with the Honda flux model of 1.5σ. This is the most precise measurement ever to experimentally determine the cosmic-ray muon polarization near 1 TeV/c. These measurement results are useful to improve atmospheric neutrino simulations.

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Papers, etc., Registered in KOARA 【 Display / hide 】

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Research Projects of Competitive Funds, etc. 【 Display / hide 】

  • Improvement of Low-Energy Event Selection at a Water Cherenkov Detector toward Proton Decay Searches

    2023.04
    -
    2026.03

    基盤研究(C), Principal investigator

  • 新光検出システム確立で目指す大型ニュートリノ・核子崩壊検出装置の高性能化

    2018.04
    -
    2020.03

    MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Early-Career Scientists , Principal investigator

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Courses Taught 【 Display / hide 】

  • PHYSICS SEMINAR 2

    2025

  • PHYSICS LABORATORIES 2

    2025

  • PHYSICS LABORATORIES 1

    2025

  • LITERATURE OF PHYSICS

    2025

  • LABORATORY IN SCIENCE

    2025

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