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Neutron Tagging following Atmospheric Neutrino Events in a Water Cherenkov Detector
Authors:
K. Abe,
Y. Haga,
Y. Hayato,
K. Hiraide,
K. Ieki,
M. Ikeda,
S. Imaizumi,
K. Iyogi,
J. Kameda,
Y. Kanemura,
Y. Kataoka,
Y. Kato,
Y. Kishimoto,
S. Miki,
S. Mine,
M. Miura,
T. Mochizuki,
S. Moriyama,
Y. Nagao,
M. Nakahata,
T. Nakajima,
Y. Nakano,
S. Nakayama,
T. Okada,
K. Okamoto
, et al. (281 additional authors not shown)
Abstract:
We present the development of neutron-tagging techniques in Super-Kamiokande IV using a neural network analysis. The detection efficiency of neutron capture on hydrogen is estimated to be 26%, with a mis-tag rate of 0.016 per neutrino event. The uncertainty of the tagging efficiency is estimated to be 9.0%. Measurement of the tagging efficiency with data from an Americium-Beryllium calibration agr…
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We present the development of neutron-tagging techniques in Super-Kamiokande IV using a neural network analysis. The detection efficiency of neutron capture on hydrogen is estimated to be 26%, with a mis-tag rate of 0.016 per neutrino event. The uncertainty of the tagging efficiency is estimated to be 9.0%. Measurement of the tagging efficiency with data from an Americium-Beryllium calibration agrees with this value within 10%. The tagging procedure was performed on 3,244.4 days of SK-IV atmospheric neutrino data, identifying 18,091 neutrons in 26,473 neutrino events. The fitted neutron capture lifetime was measured as 218 \pm 9 μs.
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Submitted 20 September, 2022; v1 submitted 18 September, 2022;
originally announced September 2022.
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First Gadolinium Loading to Super-Kamiokande
Authors:
K. Abe,
C. Bronner,
Y. Hayato,
K. Hiraide,
M. Ikeda,
S. Imaizumi,
J. Kameda,
Y. Kanemura,
Y. Kataoka,
S. Miki,
M. Miura,
S. Moriyama,
Y. Nagao,
M. Nakahata,
S. Nakayama,
T. Okada,
K. Okamoto,
A. Orii,
G. Pronost,
H. Sekiya,
M. Shiozawa,
Y. Sonoda,
Y. Suzuki,
A. Takeda,
Y. Takemoto
, et al. (192 additional authors not shown)
Abstract:
In order to improve Super-Kamiokande's neutron detection efficiency and to thereby increase its sensitivity to the diffuse supernova neutrino background flux, 13 tons of $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ (gadolinium sulfate octahydrate) was dissolved into the detector's otherwise ultrapure water from July 14 to August 17, 2020, marking the start of the SK-Gd phase of operations. During the loa…
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In order to improve Super-Kamiokande's neutron detection efficiency and to thereby increase its sensitivity to the diffuse supernova neutrino background flux, 13 tons of $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ (gadolinium sulfate octahydrate) was dissolved into the detector's otherwise ultrapure water from July 14 to August 17, 2020, marking the start of the SK-Gd phase of operations. During the loading, water was continuously recirculated at a rate of 60 m$^3$/h, extracting water from the top of the detector and mixing it with concentrated $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ solution to create a 0.02% solution of the Gd compound before injecting it into the bottom of the detector. A clear boundary between the Gd-loaded and pure water was maintained through the loading, enabling monitoring of the loading itself and the spatial uniformity of the Gd concentration over the 35 days it took to reach the top of the detector. During the subsequent commissioning the recirculation rate was increased to 120 m$^3$/h, resulting in a constant and uniform distribution of Gd throughout the detector and water transparency equivalent to that of previous pure-water operation periods. Using an Am-Be neutron calibration source the mean neutron capture time was measured to be $115\pm1$ $μ$s, which corresponds to a Gd concentration of $111\pm2$ ppm, as expected for this level of Gd loading. This paper describes changes made to the water circulation system for this detector upgrade, the Gd loading procedure, detector commissioning, and the first neutron calibration measurements in SK-Gd.
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Submitted 15 December, 2021; v1 submitted 1 September, 2021;
originally announced September 2021.
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Search for solar electron anti-neutrinos due to spin-flavor precession in the Sun with Super-Kamiokande-IV
Authors:
Super-Kamiokande Collaboration,
:,
K. Abe,
C. Bronner,
Y. Hayato,
M. Ikeda,
S. Imaizumi,
H. Ito,
J. Kameda,
Y. Kataoka,
M. Miura,
S. Moriyama,
Y. Nagao,
M. Nakahata,
Y. Nakajima,
S. Nakayama,
T. Okada,
K. Okamoto,
A. Orii,
G. Pronost,
H. Sekiya,
M. Shiozawa,
Y. Sonoda,
Y. Suzuki,
A. Takeda
, et al. (177 additional authors not shown)
Abstract:
Due to a very low production rate of electron anti-neutrinos ($\barν_e$) via nuclear fusion in the Sun, a flux of solar $\barν_e$ is unexpected. An appearance of $\barν_e$ in solar neutrino flux opens a new window for the new physics beyond the standard model. In particular, a spin-flavor precession process is expected to convert an electron neutrino into an electron anti-neutrino (…
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Due to a very low production rate of electron anti-neutrinos ($\barν_e$) via nuclear fusion in the Sun, a flux of solar $\barν_e$ is unexpected. An appearance of $\barν_e$ in solar neutrino flux opens a new window for the new physics beyond the standard model. In particular, a spin-flavor precession process is expected to convert an electron neutrino into an electron anti-neutrino (${ν_e\to\barν_e}$) when neutrino has a finite magnetic moment. In this work, we have searched for solar $\barν_e$ in the Super-Kamiokande experiment, using neutron tagging to identify their inverse beta decay signature. We identified 78 $\barν_e$ candidates for neutrino energies of 9.3 to 17.3 MeV in 2970.1 live days with a fiducial volume of 22.5 kiloton water (183.0 kton$\cdot$year exposure). The energy spectrum has been consistent with background predictions and we thus derived a 90% confidence level upper limit of ${4.7\times10^{-4}}$ on the $ν_e\to\barν_e$ conversion probability in the Sun. We used this result to evaluate the sensitivity of future experiments, notably the Super-Kamiokande Gadolinium (SK-Gd) upgrade.
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Submitted 17 March, 2022; v1 submitted 7 December, 2020;
originally announced December 2020.
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Measurement of $γ$-ray production via the neutron-$^{16}$O reaction using a 77 MeV quasi-monoenergetic neutron beam
Authors:
Y. Ashida,
H. Nagata,
M. Mori,
G. Collazuol,
D. Fukuda,
T. Horai,
F. Iacob,
A. Konaka,
Y. Koshio,
T. Nakaya,
C. Nantais,
T. Shima,
A. Suzuki,
Y. Takeuchi,
H. Tanaka,
R. Wendell,
T. Yano
Abstract:
Understanding of $γ$-ray production via neutron interactions on oxygen is essential for the study of neutrino neutral-current quasielastic interactions in water Cherenkov detectors. A measurement of $γ$-ray production from such reactions was performed using a 77~MeV quasi-monoenergetic neutron beam. Several $γ$-ray peaks, which are expected to come from neutron-${\rm ^{16}O}$ reactions, are observ…
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Understanding of $γ$-ray production via neutron interactions on oxygen is essential for the study of neutrino neutral-current quasielastic interactions in water Cherenkov detectors. A measurement of $γ$-ray production from such reactions was performed using a 77~MeV quasi-monoenergetic neutron beam. Several $γ$-ray peaks, which are expected to come from neutron-${\rm ^{16}O}$ reactions, are observed and production cross sections are measured for nine $γ$-ray components of energies between 2 and 8~MeV. These are the first measurements at this neutron energy using a nearly monoenergetic beam.
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Submitted 4 January, 2024; v1 submitted 24 February, 2019;
originally announced February 2019.