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Griskevich, N. J.

Publications and source records attributed to Griskevich, N. J..

15 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

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

We present the results of the charge ratio (𝑅) and polarization (𝑃$^{𝜇}_{0}$) 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 𝐸 𝜇 ⁢cos⁡𝜃 Zenith = 0.7$^{+0.3}_{−0.2}$ TeV, where 𝐸 𝜇 is the muon energy and 𝜃 Zenith is the zenith angle of incoming cosmic-ray muons. This result is consistent with the Honda flux model while indicating a tension with the 𝜋⁢𝐾 model of 1.9⁢𝜎. We also measured the muon polarization at the production location to be 𝑃$^{𝜇}_{0}$ = 0.52 ± 0.02 (stat+syst) at the muon momentum of 0.9$^{+0.6}_{−0.1}$ TeV/𝑐 at the surface of the mountain; this also suggests a tension with the Honda flux model of 1.5⁢𝜎. 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.

Atmospheric neutrino oscillations↗
DOE OSTI2024

New methods and simulations for cosmogenic induced spallation removal in Super-Kamiokande-IV

Radioactivity induced by cosmic muon spallation is a dominant source of backgrounds for 𝒪⁡(10 MeV) neutrino interactions in water Cherenkov detectors. In particular, it is crucial to reduce backgrounds to measure the solar neutrino spectrum and find neutrino interactions from distant supernovae. In this paper we introduce new techniques to locate muon-induced hadronic showers and efficiently reject spallation backgrounds. Applying these techniques to the solar neutrino analysis with an exposure of 2790 × 22.5 kton · day increases the signal efficiency by 12.6%, approximately corresponding to an additional year of detector running. Furthermore, we present the first spallation simulation at Super-Kamiokande, where we model hadronic interactions using fluka. The agreement between the isotope yields and shower pattern in this simulation and in the data gives confidence in the accuracy of this simulation, and thus opens the door to use it to optimize muon spallation removal in new data with gadolinium-enhanced neutron capture detection.

muons↗
DOE OSTI2024

Search for Periodic Time Variations of the Solar 8 B Neutrino Flux between 1996 and 2018 in Super-Kamiokande

We report a search for time variations of the solar 8 B neutrino flux using 5804 live days of Super-Kamiokande data collected between May 31, 1996, and May 30, 2018. Super-Kamiokande measured the precise time of each solar neutrino interaction over 22 calendar years to search for solar neutrino flux modulations with unprecedented precision. Periodic modulations are searched for in a dataset comprising five-day interval solar neutrino flux measurements with a maximum likelihood method. We also applied the Lomb-Scargle method to this dataset to compare it with previous reports. The only significant modulation found is due to the elliptic orbit of the Earth around the Sun. The observed modulation is consistent with astronomical data: we measured an eccentricity of (1.53 ± 0.35)%, and a perihelion shift of (−1.5 ± 13.5) days.

astroparticle detectors↗
DOE OSTI2024

Atmospheric neutrino oscillation analysis with neutron tagging and an expanded fiducial volume in Super-Kamiokande I–V

We present a measurement of neutrino oscillation parameters with the Super-Kamiokande detector using atmospheric neutrinos from the complete pure-water SK I–V (April 1996–July 2020) dataset, including events from an expanded fiducial volume. The dataset corresponds to 6511.3 live days and an exposure of 484.2 kiloton-years. Measurements of the neutrino oscillation parameters Δ⁢𝑚$^2_{3⁢2}$, sin 2 ⁡𝜃 2⁢3 , sin 2⁡ 𝜃 1⁢3 , 𝛿 CP , and the preference for the neutrino mass ordering are presented with atmospheric neutrino data alone, and with constraints on sin 2 ⁡𝜃 1⁢3 from reactor neutrino experiments. Our analysis including constraints on sin 2 ⁡𝜃 1⁢3 favors the normal mass ordering at the 92.3% level.

Cherenkov detectors↗
DOE OSTI2024

Measurement of the neutrino-oxygen neutral-current quasielastic cross section using atmospheric neutrinos in the SK-Gd experiment

We report the first measurement of the atmospheric neutrino-oxygen neutral-current quasielastic (NCQE) cross section in the gadolinium-loaded Super-Kamiokande (SK) water Cherenkov detector. In June 2020, SK began a new experimental phase, named SK-Gd, by loading 0.011% by mass of gadolinium into the ultrapure water of the SK detector. The introduction of gadolinium to ultrapure water has the effect of improving the neutron-tagging efficiency. Using a 552.2 day dataset from August 2020 to June 2022, we measure the NCQE cross section to be 0.74 ± 0.22 ( stat ) − 0.15 + 0.85 ( syst ) × 10 − 38 cm 2 / oxygen in the energy range from 160 MeV to 10 GeV, which is consistent with the atmospheric neutrino-flux-averaged theoretical NCQE cross section and the measurement in the SK pure-water phase within the uncertainties. Furthermore, we compare the models of the nucleon-nucleus interactions in water and find that the binary cascade model and the Liège intranuclear cascade model provide a somewhat better fit to the observed data than the Bertini cascade model. Since the atmospheric neutrino-oxygen NCQE reactions are one of the main backgrounds in the search for diffuse supernova neutrino background (DSNB), these new results will contribute to future studies—and the potential discovery—of the DSNB in SK. Published by the American Physical Society 2024

Sakai, S. (ORCID:0000000221900062)↗
DOE OSTI2022

Neutron tagging following atmospheric neutrino events in a water Cherenkov detector

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±9 μs.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Search for proton decay via p → μ + K 0 in 0.37 megaton-years exposure of Super-Kamiokande

We searched for proton decay via p → μ + K 0 in 0.37 Mton · years of data collected between 1996 and 2018 from the Super-Kamiokande water Cherenkov experiment. The selection criteria were defined separately for K$^0_S$ and K$^0_L$ channels. No significant event excess has been observed. As a result of this analysis, which extends the previous search by an additional 0.2 Mton · years of exposure and uses an improved event reconstruction, we set a lower limit of 3.6 × 10 33 years on the proton lifetime.

79 ASTRONOMY AND ASTROPHYSICS↗