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Megias, G. D.

Publications and source records attributed to Megias, G. D..

8 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 (๐‘…) and polarization (๐‘ƒ$^{๐œ‡}_{0}$) 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 ๐‘… = 1.32 ยฑ 0.02โข(stat +syst) at ๐ธ ๐œ‡ โขcosโก๐œƒ Zenith = 0.7$^{+0.3}_{โˆ’0.2}$ TeV, where ๐ธ ๐œ‡ is the muon energy and ๐œƒ 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 ๐œ‹โข๐พ model of 1.9โข๐œŽ. We also measured the muon polarization at the production location to be ๐‘ƒ$^{๐œ‡}_{0}$ = 0.52 ยฑ 0.02 (stat+syst) at the muon momentum of 0.9$^{+0.6}_{โˆ’0.1}$ TeV/๐‘ at the surface of the mountain; this also suggests a tension with the Honda flux model of 1.5โข๐œŽ. This is the most precise measurement ever to experimentally determine the cosmic-ray muon polarization near 1 TeV/๐‘. These measurement results are useful to improve atmospheric neutrino simulations.

Atmospheric neutrino oscillationsโ†—
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 ๐’ชโก(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 ร— 22.5 kton ยท 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.

muonsโ†—
DOE OSTI2023

Search for Astrophysical Electron Antineutrinos in Super-Kamiokande with 0.01% Gadolinium-loaded Water

We report the first search result for the flux of astrophysical electron antineutrinos for energies $\mathcal{O}$(10)$MeV$ in the gadolinium-loaded Super-Kamiokande (SK) detector. In 2020 June, gadolinium was introduced to the ultrapure water of the SK detector in order to detect neutrons more efficiently. In this new experimental phase, SK-Gd, we can search for electron antineutrinos via inverse beta decay with efficient background rejection thanks to the high efficiency of the neutron tagging technique. In this paper, we report the result for the initial stage of SK-Gd, during 2020 August 26, and 2022 June 1 with a 22.5 ร— 552 kton ยท day exposure at 0.01% Gd mass concentration. No significant excess over the expected background in the observed events is found for the neutrino energies below 31.3 MeV. Thus, the flux upper limits are placed at the 90% confidence level. The limits and sensitivities are already comparable with the previous SK result with pure water (22.5 ร— 2970 kton ยท day) owing to the enhanced neutron tagging. Operation with Gd increased to 0.03% started in 2022 June.

79 ASTRONOMY AND ASTROPHYSICSโ†—
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 218ยฑ9 ฮผs.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND โ†—
DOE OSTI2022

Search for proton decay via p โ†’ ฮผ + K 0 in 0.37 megaton-years exposure of Super-Kamiokande

We searched for proton decay via p โ†’ ฮผ + K 0 in 0.37 Mton ยท 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 ยท years of exposure and uses an improved event reconstruction, we set a lower limit of 3.6 ร— 10 33 years on the proton lifetime.

79 ASTRONOMY AND ASTROPHYSICSโ†—