72 research outputs found
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
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
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
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
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 Δm322, sin2θ23, sin2θ13, δCP, and the preference for the neutrino mass ordering are presented with atmospheric neutrino data alone, and with constraints on sin2θ13 from reactor neutrino experiments. Our analysis including constraints on sin2θ13 favors the normal mass ordering at the 92.3% level
Performance of SK-Gd’s upgraded real-time supernova monitoring system
Among multimessenger observations of the next Galactic core-collapse supernova, Super-Kamiokande (SK) plays a critical role in detecting the emitted supernova neutrinos, determining the direction to the supernova (SN), and notifying the astronomical community of these observations in advance of the optical signal. In 2022, SK has increased the gadolinium dissolved in its water target (SK-Gd) and has achieved a Gd concentration of 0.033%, resulting in enhanced neutron detection capability, which in turn enables more accurate determination of the supernova direction. Accordingly, SK-Gd's real-time supernova monitoring system has been upgraded. SK_SN Notice, a warning system that works together with this monitoring system, was released on 2021 December 13, and is available through GCN Notices. When the monitoring system detects an SN-like burst of events, SK_SN Notice will automatically distribute an alarm with the reconstructed direction to the supernova candidate within a few minutes. In this paper, we present a systematic study of SK-Gd's response to a simulated Galactic SN. Assuming a supernova situated at 10 kpc, neutrino fluxes from six supernova models are used to characterize SK-Gd's pointing accuracy using the same tools as the online monitoring system. The pointing accuracy is found to vary from 3° to 7° depending on the models. However, if the supernova is closer than 10 kpc, SK_SN Notice can issue an alarm with three-degree accuracy, which will benefit follow-up observations by optical telescopes with large fields of view
Measurements of the νμ and ν¯μ -induced coherent charged pion production cross sections on C12 by the T2K experiment
We report an updated measurement of the
ν
μ
-induced, and the first measurement of the
¯
ν
μ
-induced coherent charged pion production cross section on
12
C
nuclei in the Tokai-to-Kamioka experiment. This is measured in a restricted region of the final-state phase space for which
p
μ
,
π
>
0.2
GeV
,
cos
(
θ
μ
)
>
0.8
and
cos
(
θ
π
)
>
0.6
, and at a mean (anti)neutrino energy of 0.85 GeV using the T2K near detector. The measured
ν
μ
charged current coherent pion production flux-averaged cross section on
12
C
is
(
2.98
±
0.37
(
stat
)
±
0.31
(
syst
)
+
0.49
−
0.00
(
Q
2
model
)
)
×
10
−
40
cm
2
. The new measurement of the
¯
ν
μ
-induced cross section on
12
C
is
(
3.05
±
0.71
(
stat
)
±
0.39
(
syst
)
+
0.74
−
0.00
(
Q
2
model
)
)
×
10
−
40
cm
2
. The results are compatible with both the NEUT 5.4.0 Berger-Sehgal (2009) and GENIE 2.8.0 Rein-Sehgal (2007) model predictions
Performance of SK-Gd's upgraded real-time supernova monitoring system
Among multi-messenger observations of the next galactic core-collapse supernova, Super-Kamiokande (SK) plays a critical role in detecting the emitted supernova neutrinos, determining the direction to the supernova (SN), and notifying the astronomical community of these observations in advance of the optical signal. On 2022, SK has increased the gadolinium dissolved in its water target (SK-Gd) and has achieved a Gd concentration of 0.033%, resulting in enhanced neutron detection capability, which in turn enables more accurate determination of the supernova direction. Accordingly, SK-Gd's real-time supernova monitoring system (Abe te al. 2016b) has been upgraded. SK_SN Notice, a warning system that works together with this monitoring system, was released on December 13, 2021, and is available through GCN Notices (Barthelmy et al. 2000). When the monitoring system detects an SN-like burst of events, SK_SN Notice will automatically distribute an alarm with the reconstructed direction to the supernova candidate within a few minutes. In this paper, we present a systematic study of SK-Gd's response to a simulated galactic SN. Assuming a supernova situated at 10 kpc, neutrino fluxes from six supernova models are used to characterize SK-Gd's pointing accuracy using the same tools as the online monitoring system. The pointing accuracy is found to vary from 3-7∘ depending on the models. However, if the supernova is closer than 10 kpc, SK_SN Notice can issue an alarm with three-degree accuracy, which will benefit follow-up observations by optical telescopes with large fields of view
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 (Pμ0) measurements using the decay electron events collected from 2008 September to 2022 June by the Super-Kamiokande detector. Because of its underground location and long operation, we performed 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+0.3−0.2 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 this suggests a tension with the πK model of 1.9σ. We also measured the muon polarization at the production location to be Pμ0=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 1.5σ. 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 the atmospheric neutrino simulations
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