Phys. Rev. D 103, 012008 (2021) As a baryon number violating process with $\Delta B=2$, neutron-antineutron
oscillation ($n\to\bar n$) provides a unique test of baryon number
conservation. We have ...performed a search for $n\to\bar n$ oscillation with
bound neutrons in Super-Kamiokande, with the full data set from its first four
run periods, representing an exposure of 0.37~Mton-years. The search used a
multivariate analysis trained on simulated $n\to\bar n$ events and atmospheric
neutrino backgrounds and resulted in 11 candidate events with an expected
background of 9.3 events. In the absence of statistically significant excess,
we derived a lower limit on $\bar n$ appearance lifetime in $^{16}$O nuclei of
$3.6\times{10}^{32}$ years and on the neutron-antineutron oscillation time of
$\tau_{n\to\bar n} > 4.7\times10^{8}$~s at 90\% C.L..
Phys. Rev. D 102, 112011 (2020) We have searched for proton decay via $p\to e^+\pi^0$ and $p\to \mu^+\pi^0$
modes with the enlarged fiducial volume data of Super-Kamiokande from April
1996 to May ...2018, which corresponds to 450 kton$\cdot$years exposure. We have
accumulated about 25% more livetime and enlarged the fiducial volume of the
Super-Kamiokande detector from 22.5 kton to 27.2 kton for this analysis, so
that 144 kton$\cdot$years of data, including 78 kton$\cdot$years of additional
fiducial volume data, has been newly analyzed. No candidates have been found
for $p\to e^+\pi^0$ and one candidate remains for $p\to \mu^+\pi^0$ in the
conventional 22.5 kton fiducial volume and it is consistent with the
atmospheric neutrino background prediction. We set lower limits on the partial
lifetime for each of these modes: $\tau/B(p\to e^+\pi^0) > 2.4 \times 10^{34}$
years and $\tau/B(p\to \mu^+\pi^0) > 1.6 \times 10^{34}$ years at 90%
confidence level.
An upgrade of the Near Detector of the T2K long baseline neutrino oscillation experiment, ND280, has been proposed. This upgrade will include two new Time Projection Chambers, each equipped with 16 ...resistive MicroMegas modules for gas amplification. A first prototype of resistive MicroMegas has been designed, built, installed in the HARP field cage, and exposed to a beam of charged particles at CERN. The data have been used to characterize the performances of the resistive MicroMegas module. A spatial resolution of 300 \(\mu m\) and a deposited energy resolution of 9% were observed for horizontal electrons crossing the TPCs at 30 cm from the anode. Such performances fully satisfy the requirements for the upgrade of the ND280 TPC.
A search for proton decay into three charged leptons has been performed by using 0.37\(\,\)Mton\(\cdot\)years of data collected in Super-Kamiokande. All possible combinations of electrons, muons and ...their anti-particles consistent with charge conservation were considered as decay modes. No significant excess of events has been found over the background, and lower limits on the proton lifetime divided by the branching ratio have been obtained. The limits range between \(9.2\times10^{33}\) to \(3.4\times10^{34}\) years at 90\(\,\)% confidence level, improving by more than an order of magnitude upon limits from previous experiments. A first limit has been set for the \(p\rightarrow\mu^-e^+e^+\) mode.
We report a search for astronomical neutrinos in the energy region from several GeV to TeV in the direction of the blazar TXS0506+056 using the Super-Kamiokande detector following the detection of a ...100 TeV neutrino from the same location by the IceCube collaboration. Using Super-Kamiokande neutrino data across several data samples observed from April 1996 to February 2018 we have searched for both a total excess above known backgrounds across the entire period as well as localized excesses on smaller time scales in that interval. No significant excess nor significant variation in the observed event rate are found in the blazar direction. Upper limits are placed on the electron and muon neutrino fluxes at 90\% confidence level as \(6.03 \times 10^{-7}\) and \(4.52 \times 10^{-7}\) to \(9.26 \times 10^{-10}\) \({\rm erg}/{\rm cm}^2/{\rm s}\), respectively.
Neutral current (NC) interactions of atmospheric neutrinos on oxygen form one of the major backgrounds in the search for supernova relic neutrinos with water-based Cherenkov detectors. The NC channel ...is dominated by neutrino quasi-elastic (NCQE) scattering off nucleons inside \(^{16}\)O nuclei. In this paper we report the first measurement of NCQE cross section using atmospheric neutrinos at Super-Kamiokande (SK). The measurement used 2,778 live days of SK-IV data with a fiducial volume of 22.5 kiloton water. Within the visible energy window of 7.5-29.5 MeV, we observed \(117\) events compared to the expected \(71.9\) NCQE signal and \(53.1\) background events. Weighted by the atmospheric neutrino spectrum from 160 MeV to 10 GeV, the flux averaged NCQE cross section is measured to be \((1.01\pm0.17(\text{stat.})^{+0.78}_{-0.30}(\text{sys.}))\times10^{-38}\) cm\(^2\).
A new event reconstruction algorithm based on a maximum likelihood method has been developed for Super-Kamiokande. Its improved kinematic and particle identification capabilities enable the analysis ...of atmospheric neutrino data in a detector volume 32% larger than previous analyses and increases sensitivity to the neutrino mass hierarchy. Analysis of a 253.9 kton-year exposure of the Super-Kamiokande IV atmospheric neutrino data has yielded a weak preference for the normal hierarchy, disfavoring the inverted hierarchy at 74% assuming oscillations at the best fit of the analysis.
Using 0.37 megaton\(\cdot\)years of exposure from the Super-Kamiokande detector, we search for 10 dinucleon and nucleon decay modes that have a two-body final state with no hadrons. These baryon and ...lepton number violating modes have the potential to probe theories of unification and baryogenesis. For five of these modes the searches are novel, and for the other five modes we improve the limits by more than one order of magnitude. No significant evidence for dinucleon or nucleon decay is observed and we set lower limits on the partial lifetime of oxygen nuclei and on the nucleon partial lifetime that are above \(4\times 10^{33}\) years for oxygen via the dinucleon decay modes and up to about \(4 \times 10^{34}\) years for nucleons via the single nucleon decay modes.
Understanding of \(\gamma\)-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 \(\gamma\)-ray production from such reactions was performed using a 77~MeV quasi-monoenergetic neutron beam. Several \(\gamma\)-ray peaks, which are expected to come from neutron-\({\rm ^{16}O}\) reactions, are observed and production cross sections are measured for nine \(\gamma\)-ray components of energies between 2 and 8~MeV. These are the first measurements at this neutron energy using a nearly monoenergitic beam.
As a baryon number violating process with \(\Delta B=2\), neutron-antineutron oscillation (\(n\to\bar n\)) provides a unique test of baryon number conservation. We have performed a search for ...\(n\to\bar n\) oscillation with bound neutrons in Super-Kamiokande, with the full data set from its first four run periods, representing an exposure of 0.37~Mton-years. The search used a multivariate analysis trained on simulated \(n\to\bar n\) events and atmospheric neutrino backgrounds and resulted in 11 candidate events with an expected background of 9.3 events. In the absence of statistically significant excess, we derived a lower limit on \(\bar n\) appearance lifetime in \(^{16}\)O nuclei of \(3.6\times{10}^{32}\) years and on the neutron-antineutron oscillation time of \(\tau_{n\to\bar n} > 4.7\times10^{8}\)~s at 90\% C.L..
