152 research outputs found
A case report of pulmonary tumor thrombotic microangiopathy (PTTM) caused by esophageal squamous cell carcinoma
Search for Cosmic-ray Boosted Sub-GeV Dark Matter using Recoil Protons at Super-Kamiokande
We report a search for cosmic-ray boosted dark matter with protons using the
0.37 megatonyears data collected at Super-Kamiokande experiment during
the 1996-2018 period (SKI-IV phase). We searched for an excess of proton
recoils above the atmospheric neutrino background from the vicinity of the
Galactic Center. No such excess is observed, and limits are calculated for two
reference models of dark matter with either a constant interaction
cross-section or through a scalar mediator. This is the first experimental
search for boosted dark matter with hadrons using directional information. The
results present the most stringent limits on cosmic-ray boosted dark matter and
exclude the dark matter-nucleon elastic scattering cross-section between
and for dark matter mass
from 10 MeV/ to 1 GeV/.Comment: With 1-page appendi
Search for Periodic Time Variations of the Solar B Neutrino Flux Between 1996 and 2018 in Super-Kamiokande
We report a search for time variations of the solar B neutrino flux using
5,804 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 data set comprised of five-day interval solar neutrino flux measurements
with a maximum likelihood method. We also applied the Lomb-Scargle method to
this data set 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 (1.530.35)\,\%, and a perihelion shift is
(1.513.5)\,days.Comment: 8 pages, 5 figures, 2 tables, and data file:
"sksolartimevariation5804d.txt
Measurement of the cosmogenic neutron yield in Super-Kamiokande with gadolinium loaded water
Cosmic-ray muons that enter the Super-Kamiokande detector cause hadronic
showers due to spallation in water, producing neutrons and radioactive
isotopes. Those are a major background source for studies of MeV-scale
neutrinos and searches for rare events. Since 2020, gadolinium was introduced
in the ultra-pure water in the Super-Kamiokande detector to improve the
detection efficiency of neutrons. In this study, the cosmogenic neutron yield
was measured using data acquired during the period after the gadolinium
loading. The yield was found to be at
259 GeV of average muon energy at the Super-Kamiokande detector.Comment: 10 pages, 10 figures, 3 table
Search for astrophysical electron antineutrinos in Super-Kamiokande with 0.01wt% gadolinium-loaded water
We report the first search result for the flux of astrophysical electron
antineutrinos for energies O(10) MeV in the gadolinium-loaded Super-Kamiokande
(SK) detector. In June 2020, gadolinium was introduced to the ultra-pure 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 and higher signal efficiency
thanks to the high efficiency of the neutron tagging technique. In this paper,
we report the result for the initial stage of SK-Gd with a 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 () owing
to the enhanced neutron tagging
Measurement of neutrino and antineutrino neutral-current quasielasticlike interactions on oxygen by detecting nuclear deexcitation Îł rays
Neutrino- and antineutrino-oxygen neutral-current quasielastic-like
interactions are measured at Super-Kamiokande using nuclear de-excitation
-rays to identify signal-like interactions in data from a $14.94 \
(16.35)\times 10^{20}\langle \sigma_{\nu {\rm -NCQE}} \rangle = 1.70 \pm 0.17 ({\rm stat.}) ^{+
{\rm 0.51}}_{- {\rm 0.38}} ({\rm syst.}) \times 10^{-38} \ {\rm cm^2/oxygen}\langle \sigma_{\bar{\nu} {\rm
-NCQE}} \rangle = 0.98 \pm 0.16 ({\rm stat.}) ^{+ {\rm 0.26}}_{- {\rm 0.19}}
({\rm syst.}) \times 10^{-38} \ {\rm cm^2/oxygen}$ with a flux-averaged energy
of 0.68 GeV, for neutrinos and antineutrinos, respectively. These results are
the most precise to date, and the antineutrino result is the first cross
section measurement of this channel. They are compared with various theoretical
predictions. The impact on evaluation of backgrounds to searches for supernova
relic neutrinos at present and future water Cherenkov detectors is also
discussed
Measurements of the and -induced Coherent Charged Pion Production Cross Sections on by the T2K experiment
We report an updated measurement of the -induced, and the first
measurement of the -induced coherent charged pion production
cross section on nuclei in the T2K experiment. This is measured in a
restricted region of the final-state phase space for which
GeV, and , and at a mean
(anti)neutrino energy of 0.85 GeV using the T2K near detector. The measured
CC coherent pion production flux-averaged cross section on
is . The new measurement
of the -induced cross section on is . The results are compatible with both the NEUT
5.4.0 Berger-Sehgal (2009) and GENIE 2.8.0 Rein-Sehgal (2007) model
predictions
Search for electron antineutrino appearance in a long-baseline muon antineutrino beam
Electron antineutrino appearance is measured by the T2K experiment in an accelerator-produced antineutrino beam, using additional neutrino beam operation to constrain parameters of the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix. T2K observes 15 candidate electron antineutrino events with a background expectation of 9.3 events. Including information from the kinematic distribution of observed events, the hypothesis of no electron antineutrino appearance is disfavored with a significance of 2.40Ï and no discrepancy between data and PMNS predictions is found. A complementary analysis that introduces an additional free parameter which allows non-PMNS values of electron neutrino and antineutrino appearance also finds no discrepancy between data and PMNS predictions
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