Publications
294 results found
Blondel A, Bogomilov M, Bordoni S, et al., 2020, The SuperFGD Prototype charged particle beam tests, JOURNAL OF INSTRUMENTATION, Vol: 15, ISSN: 1748-0221
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Abe K, Bronner C, Haga Y, et al., 2020, Indirect search for dark matter from the Galactic Center and halo with the Super-Kamiokande detector, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 102, Pages: 072002 – 1-072002 – 14, ISSN: 1550-2368
We present a search for an excess of neutrino interactions due to dark matter in the form of weakly interacting massive particles (WIMPs) annihilating in the Galactic center or halo based on the data set of Super-Kamiokande-I, -II, -III and -IV taken from 1996 to 2016. We model the neutrino flux, energy, and flavor distributions assuming WIMP self-annihilation is dominant to ν¯ν, μ+μ−, b¯b, or W+W−. The excess is in comparison to atmospheric neutrino interactions which are modeled in detail and fit to data. Limits on the self-annihilation cross section ⟨σAV⟩ are derived for WIMP masses in the range 1 GeV to 10 TeV, reaching as low as 9.6×10−23 cm3 s−1 for 5 GeV WIMPs in b¯b mode and 1.2×10−24 cm3 s−1 for 1 GeV WIMPs in ν¯ν mode. The obtained sensitivity of the Super-Kamiokande detector to WIMP masses below several tens of GeV is the best among similar indirect searches to date.
Abe K, Akhlaq N, Akutsu R, et al., 2020, Measurement of the charged-current electron (anti-)neutrino inclusive cross-sections at the T2K off-axis near detector ND280, The Journal of High Energy Physics, Vol: 2020, Pages: 1-43, ISSN: 1029-8479
The electron (anti-)neutrino component of the T2K neutrino beam constitutes the largest background in the measurement of electron (anti-)neutrino appearance at the far detector. The electron neutrino scattering is measured directly with the T2K off-axis near detector, ND280. The selection of the electron (anti-)neutrino events in the plastic scintillator target from both neutrino and anti-neutrino mode beams is discussed in this paper. The flux integrated single differential charged-current inclusive electron (anti-)neutrino cross-sections, dσ/dp and dσ/d cos(θ), and the total cross-sections in a limited phase-space in momentum and scattering angle (p > 300 MeV/c and θ ≤ 45°) are measured using a binned maximum likelihood fit and compared to the neutrino Monte Carlo generator predictions, resulting in good agreement.
Abe K, Akutsu R, Ali A, et al., 2020, First measurement of the charged current (nu)over-bar(mu) double differential cross section on a water target without( )pions in the final state, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 102, Pages: 1-16, ISSN: 1550-2368
This paper reports the first differential measurement of the charged-current ¯νμ interaction cross section on water with no pions in the final state. The unfolded flux-averaged measurement using the T2K off-axis near detector is given in double-differential bins of μ+ momentum and angle. The integrated cross section in a restricted phase space is σ=(1.11±0.18)×10−38 cm2 per water molecule. Comparisons with several nuclear models are also presented.
Abe K, Akhlaq N, Akutsu R, et al., 2020, Simultaneous measurement of the muon neutrino charged-current cross section on oxygen and carbon without pions in the final state at T2K, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 101, Pages: 112004 – 1-112004 – 32, ISSN: 1550-2368
This paper reports the first simultaneous measurement of the double differential muon neutrino charged-current cross section on oxygen and carbon without pions in the final state as a function of the outgoing muon kinematics, made at the ND280 off-axis near detector of the T2K experiment. The ratio of the oxygen and carbon cross sections is also provided to help validate various models’ ability to extrapolate between carbon and oxygen nuclear targets, as is required in T2K oscillation analyses. The data are taken using a neutrino beam with an energy spectrum peaked at 0.6 GeV. The extracted measurement is compared with the prediction from different Monte Carlo neutrino-nucleus interaction event generators, showing particular model separation for very forward-going muons. Overall, of the models tested, the result is best described using local Fermi gas descriptions of the nuclear ground state with RPA suppression.
Abe K, Akhlaq N, Akutsu R, et al., 2020, First combined measurement of the muon neutrino and antineutrino charged-current cross section without pions in the final state at T2K, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 101, Pages: 112001 – 1-112001 – 44, ISSN: 1550-2368
This paper presents the first combined measurement of the double-differential muon neutrino and antineutrino charged-current cross sections with no pions in the final state on hydrocarbon at the off-axis near detector of the T2K experiment. The data analyzed in this work comprise 5.8×1020 and 6.3×1020 protons on target in neutrino and antineutrino mode respectively, at a beam energy peak of 0.6 GeV. Using the two measured cross sections, the sum, difference, and asymmetry were calculated with the aim of better understanding the nuclear effects involved in such interactions. The extracted measurements have been compared with the prediction from different Monte Carlo generators and theoretical models showing that the difference between the two cross sections have interesting sensitivity to nuclear effects.
Abe K, Akutsu R, Ali A, et al., 2020, Search for electron antineutrino appearance in a long-baseline muon antineutrino beam, Physical Review Letters, Vol: 124, Pages: 161802-1-161802-8, ISSN: 0031-9007
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 2.40σ 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.
Abe K, Akutsu R, Ali A, et al., 2020, Constraint on the matter-antimatter symmetry-violating phase in neutrino oscillations, Nature, Vol: 580, Pages: 339-344, ISSN: 0028-0836
The charge-conjugation and parity-reversal (CP) symmetry of fundamental particles is a symmetry between matter and antimatter. Violation of this CP symmetry was first observed in 19641, and CP violation in the weak interactions of quarks was soon established2. Sakharov proposed3 that CP violation is necessary to explain the observed imbalance of matter and antimatter abundance in the Universe. However, CP violation in quarks is too small to support this explanation. So far, CP violation has not been observed in non-quark elementary particle systems. It has been shown that CP violation in leptons could generate the matter–antimatter disparity through a process called leptogenesis4. Leptonic mixing, which appears in the standard model’s charged current interactions5,6, provides a potential source of CP violation through a complex phase δCP, which is required by some theoretical models of leptogenesis7,8,9. This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments10,11. Until now, the value of δCP has not been substantially constrained by neutrino oscillation experiments. Here we report a measurement using long-baseline neutrino and antineutrino oscillations observed by the T2K experiment that shows a large increase in the neutrino oscillation probability, excluding values of δCP that result in a large increase in the observed antineutrino oscillation probability at three standard deviations (3σ). The 3σ confidence interval for δCP, which is cyclic and repeats every 2π, is [−3.41, −0.03] for the so-called normal mass ordering and [−2.54, −0.32] for the inverted mass ordering. Our results indicate CP violation in leptons and our method enables sensitive searches for matter–antimatter
Tanaka M, Abe K, Bronner C, et al., 2020, Search for proton decay into three charged leptons in 0.37 megaton-years exposure of the Super-Kamiokande, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 101, Pages: 052011 – 1-052011 – 12, ISSN: 1550-2368
A search for proton decay into three charged leptons has been performed by using 0.37 Mton⋅years of data collected in Super-Kamiokande. All possible combinations of electrons, muons, and their antiparticles 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 9.2×1033 and 3.4×1034 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→μ−e+e+ mode.
Abramishvili R, Adamov G, Akhmetshin RR, et al., 2020, COMET phase-I technical design report, Progress of Theoretical and Experimental Physics, Vol: 2020, ISSN: 2050-3911
The Technical Design for the COMET Phase-I experiment is presented in this paper. COMET is an experiment at J-PARC, Japan, which will search for neutrinoless conversion of muons into electrons in the field of an aluminum nucleus (μ–e conversion, μ−N→e−N); a lepton flavor-violating process. The experimental sensitivity goal for this process in the Phase-I experiment is 3.1×10−15, or 90% upper limit of a branching ratio of 7×10−15, which is a factor of 100 improvement over the existing limit. The expected number of background events is 0.032. To achieve the target sensitivity and background level, the 3.2 kW 8 GeV proton beam from J-PARC will be used. Two types of detectors, CyDet and StrECAL, will be used for detecting the μ–e conversion events, and for measuring the beam-related background events in view of the Phase-II experiment, respectively. Results from simulation on signal and background estimations are also described.
Nakazawa Y, Fujii Y, Gillies E, et al., 2020, Radiation hardness study for the COMET Phase-I electronics, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol: 955, Pages: 1-7, ISSN: 0168-9002
Radiation damage on front-end readout and trigger electronics is an important issue in the COMET Phase-I experiment at J-PARC, which plans to search for the neutrinoless transition of a muon to an electron. To produce an intense muon beam, a high-power proton beam impinges on a graphite target, resulting in a high-radiation environment. We require radiation tolerance to a total dose of 1.0 kGy and 1 MeV equivalent neutron fluence of 1.0 x 10'12 neq cm-2 including a safety factor of 5 over the duration of the physics measurement. The use of commercially-available electronics components which have high radiation tolerance, if such components can be secured, is desirable in such an environment. The radiation hardness of commercial electronic components has been evaluated in gamma-ray and neutron irradiation tests. As results of these tests, voltage regulators, ADCs, DACs, and several other components were found to have enough tolerance to both gamma-ray and neutron irradiation at the level we require.
Abe K, Akutsu R, Ali A, et al., 2020, Measurement of the muon neutrino charged-current single pi(+) production on hydrocarbon using the T2K off-axis near detector ND280, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 101, ISSN: 1550-2368
We report the measurements of the single and double differential cross section of muon neutrino charged-current interactions on carbon with a single positively charged pion in the final state at the T2K off-axis near detector using 5.56×1020 protons on target. The analysis uses data control samples for the background subtraction and the cross section signal, defined as a single negatively charged muon and a single positively charged pion exiting from the target nucleus, is extracted using an unfolding method. The model-dependent cross section, integrated over the T2K off-axis neutrino beam spectrum peaking at 0.6 GeV, is measured to be σ=(11.76±0.44(stat)±2.39(syst))×10−40 cm2 nucleon−1. Various differential cross sections are measured, including the first measurement of the Adler angles for single charged pion production in neutrino interactions with heavy nuclei target.
Abe K, Akutsu R, Ali A, et al., 2019, Measurement of neutrino and antineutrino neutral-current quasielasticlike interactions on oxygen by detecting nuclear deexcitation gamma rays, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 100, Pages: 1-19, ISSN: 1550-2368
Neutrino- and antineutrino-oxygen neutral-current quasielasticlike interactions are measured at Super-Kamiokande using nuclear deexcitation γ rays to identify signal-like interactions in data from a 14.94(16.35)×1020 protons-on-target exposure of the T2K neutrino (antineutrino) beam. The measured flux-averaged cross sections on oxygen nuclei are ⟨σν−NCQE⟩=1.70±0.17(stat.)+0.51−0.38(syst.)×10−38 cm2/oxygen with a flux-averaged energy of 0.82 GeV and ⟨σ¯ν−NCQE⟩=0.98±0.16(stat.)+0.26−0.19(syst.)×10−38 cm2/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.
Hagiwara K, Abe K, Bronner C, et al., 2019, Search for astronomical neutrinos from blazar TXS 0506+056 in super-kamiokande, The Astrophysical Journal: an international review of astronomy and astronomical physics, Vol: 887, Pages: 1-7, ISSN: 0004-637X
We report a search for astronomical neutrinos in the energy region from several GeV to TeV in the direction of the blazar TXS 0506+056 using the Super-Kamiokande detector following the detection of a 100 TeV neutrinos from the same location by the IceCube collaboration. Using Super-Kamiokande neutrino data across several data samples observed from 1996 April to 2018 February we have searched for both a total excess above known backgrounds across the entire period as well as localized excesses on smaller timescales 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 the 90% confidence level as 6.0 × 10−7 and 4.5 × 10−7–9.3 × 10−10 [erg cm−2 s−1], respectively.
Simpson C, Abe K, Bronner C, et al., 2019, Sensitivity of super-kamiokande with gadolinium to low energy antineutrinos from pre-supernova emission, The Astrophysical Journal: an international review of astronomy and astronomical physics, Vol: 885, Pages: 1-14, ISSN: 0004-637X
Supernova detection is a major objective of the Super-Kamiokande (SK) experiment. In the next stage of SK (SK-Gd), gadolinium (Gd) sulfate will be added to the detector, which will improve the ability of the detector to identify neutrons. A core-collapse supernova (CCSN) will be preceded by an increasing flux of neutrinos and antineutrinos, from thermal and weak nuclear processes in the star, over a timescale of hours; some of which may be detected at SK-Gd. This could provide an early warning of an imminent CCSN, hours earlier than the detection of the neutrinos from core collapse. Electron antineutrino detection will rely on inverse beta decay events below the usual analysis energy threshold of SK, so Gd loading is vital to reduce backgrounds while maximizing detection efficiency. Assuming normal neutrino mass ordering, more than 200 events could be detected in the final 12 hr before core collapse for a 15–25 solar mass star at around 200 pc, which is representative of the nearest red supergiant to Earth, α-Ori (Betelgeuse). At a statistical false alarm rate of 1 per century, detection could be up to 10 hr before core collapse, and a pre-supernova star could be detected by SK-Gd up to 600 pc away. A pre-supernova alert could be provided to the astrophysics community following gadolinium loading.
Abe K, Akutsu R, Ali A, et al., 2019, Search for heavy neutrinos with the T2K near detector ND280, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 100, ISSN: 1550-2368
This paper reports on the search for heavy neutrinos with masses in the range 140<MN<493 MeV/c2 using the off-axis near detector ND280 of the T2K experiment. These particles can be produced from kaon decays in the standard neutrino beam and then subsequently decay in ND280. The decay modes under consideration are N→ℓ±απ∓ and N→ℓ+αℓ−β(−)ν(α,β=e,μ). A search for such events has been made using the Time Projection Chambers of ND280, where the background has been reduced to less than two events in the current dataset in all channels. No excess has been observed in the signal region. A combined Bayesian statistical approach has been applied to extract upper limits on the mixing elements of heavy neutrinos to electron-, muon- and tau- flavored currents (U2e, U2μ, U2τ) as a function of the heavy neutrino mass, e.g., U2e<10−9 at 90% C.L. for a mass of 390 MeV/c2. These constraints are competitive with previous experiments.
Abe K, Akutsu R, Ali A, et al., 2019, Measurement of the muon neutrino charged-current cross sections on water, hydrocarbon and iron, and their ratios, with the T2K on-axis detectors, Progress of Theoretical and Experimental Physics, Vol: 2019, Pages: 1-30, ISSN: 0033-068X
We report a measurement of the flux-integrated νμ charged-current cross sections on water, hydrocarbon, and iron in the T2K on-axis neutrino beam with a mean neutrino energy of 1.5 GeV. The measured cross sections on water, hydrocarbon, and iron are σH2OCC=(0.840±0.010(stat.)+0.10−0.08(syst.))×10−38cm2/nucleon, σCHCC=(0.817±0.007(stat.)+0.11−0.08(syst.))×10−38cm2/nucleon, and σFeCC=(0.859±0.003(stat.)+0.12−0.10(syst.))×10−38cm2/nucleon, respectively, for a restricted phase space of induced muons: θμ<45∘ and pμ>0.4 GeV/c in the laboratory frame. The measured cross section ratios are σH2OCC/σCHCC=1.028±0.016(stat.)±0.053(syst.), σFeCC/σH2OCC=1.023±0.012(stat.)±0.058(syst.), and σFeCC/σCHCC=1.049±0.010(stat.)±0.043(syst.). These results, with an unprecedented precision for the measurements of neutrino cross sections on water in the studied energy region, show good agreement with the current neutrino interaction models used in the T2K oscillation analyses.
Abe K, Akutsu R, Ali A, et al., 2019, Search for neutral-current induced single photon production at the ND280 near detector in T2K, Journal of Physics G: Nuclear and Particle Physics, Vol: 46, ISSN: 0954-3899
Neutrino neutral-current (NC) induced single photon production is a sub-leading order process for accelerator-based neutrino beam experiments including T2K. It is, however, an important process to understand because it is a background for electron (anti)neutrino appearance oscillation experiments. Here, we performed the first search of this process below 1 GeV using the fine-grained detector at the T2K ND280 off-axis near detector. By reconstructing single photon kinematics from electron–positron pairs, we achieved 95% pure gamma ray sample from $5.738\times {10}^{20}$ protons-on-targets neutrino mode data. We do not find positive evidence of NC induced single photon production in this sample. We set the model-dependent upper limit on the cross-section for this process, at $0.114\times {10}^{-38}$ cm2 (90% C.L.) per nucleon, using the J-PARC off-axis neutrino beam with an average energy of $\left\langle {E}_{\nu }\right\rangle \sim 0.6$ GeV. This is the first limit on this process below 1 GeV which is important for current and future oscillation experiments looking for electron neutrino appearance oscillation signals.
Jiang M, Abe K, Bronner C, et al., 2019, Atmospheric neutrino oscillation analysis with improved event reconstruction in Super-Kamiokande IV, Progress of Theoretical and Experimental Physics, Vol: 2019, ISSN: 2050-3911
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 increase the 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.
Abe K, Akutsu R, Ali A, et al., 2019, Search for light sterile neutrinos with the T2K far detector Super-Kamiokande at a baseline of 295 km, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 99, ISSN: 1550-2368
We perform a search for light sterile neutrinos using the data from the T2K far detector at a baseline of 295 km, with an exposure of 14.7(7.6)×1020 protons on target in neutrino (antineutrino) mode. A selection of neutral-current interaction samples is also used to enhance the sensitivity to sterile mixing. No evidence of sterile neutrino mixing in the 3+1 model was found from a simultaneous fit to the charged-current muon, electron and neutral-current neutrino samples. We set the most stringent limit on the sterile oscillation amplitude sin2θ24 for the sterile neutrino mass splitting Δm241<3×10−3 eV2/c4.
Wan L, Abe K, Bronner C, et al., 2019, Measurement of the neutrino-oxygen neutral-current quasielastic cross section using atmospheric neutrinos at Super-Kamiokande, Physical Review D, Vol: 99, ISSN: 2470-0010
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 quasielastic (NCQE) scattering off nucleons inside 16O 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±0.17(stat.)+0.78−0.30(sys.))×10−38 cm2.
Angélique J-C, Cârloganu C, Silva WD, et al., 2018, COMET - A submission to the 2020 update of the European Strategy for Particle Physics on behalf of the COMET collaboration
The search for charged lepton flavour violation (CLFV) has enormous discoverypotential in probing new physics Beyond the Standard Model (BSM). Among themuonic CLFV processes, $\mu \to e$ conversion is one of the most importantprocesses, having several advantages compared to other such processes. Wedescribe the COMET experiment, which is searching for $\mu \to e$ conversion ina muonic atom at the J-PARC proton accelerator laboratory in Japan. The COMETexperiment has taken a staged approach; the first stage, COMET Phase-I, iscurrently under construction at J-PARC, and is aiming at a factor 100improvement over the current limit. The second stage, COMET Phase-II is seekinganother 100 improvement (a total of 10,000), allowing a single eventsensitivity (SES) of $2.6 \times 10^{-17}$ with $2\times 10^{7}$ seconds ofdata-taking. Further improvements by one order of magnitude, which arise fromrefinements to the experimental design and operation, are being consideredwhilst staying within the originally-assumed beam power and beam time. Such asensitivity could be translated into probing many new physics constructions upto $\mathcal{O}(10^{4})$ TeV energy scales, which would go far beyond the levelthat can be reached directly by collider experiments. The search for CLFV $\mu\to e$ conversion is thus highly complementary to BSM searches at the LHC.
Collaboration S-K, Sussman S, Abe K, et al., 2018, Dinucleon and Nucleon Decay to Two-Body Final States with no Hadrons in Super-Kamiokande
Using 0.37 megaton$\cdot$years of exposure from the Super-Kamiokandedetector, we search for 10 dinucleon and nucleon decay modes that have atwo-body final state with no hadrons. These baryon and lepton number violatingmodes have the potential to probe theories of unification and baryogenesis. Forfive of these modes the searches are novel, and for the other five modes weimprove the limits by more than one order of magnitude. No significant evidencefor dinucleon or nucleon decay is observed and we set lower limits on thepartial lifetime of oxygen nuclei and on the nucleon partial lifetime that areabove $4\times 10^{33}$ years for oxygen via the dinucleon decay modes and upto about $4 \times 10^{34}$ years for nucleons via the single nucleon decaymodes.
Abe K, Akutsu R, Amey J, et al., 2018, Search for CP violation in neutrino and antineutrino oscillations by the T2K experiment with 2.2 x 10(21) protons on target, Physical Review Letters, Vol: 121, ISSN: 0031-9007
The T2K experiment measures muon neutrino disappearance and electron neutrino appearance in accelerator-produced neutrino and antineutrino beams. With an exposure of 14.7(7.6)×1020 protons on target in the neutrino (antineutrino) mode, 89 νe candidates and seven anti-νe candidates are observed, while 67.5 and 9.0 are expected for δCP=0 and normal mass ordering. The obtained 2σconfidence interval for the CP-violating phase, δCP, does not include the CP-conserving cases (δCP=0, π). The best-fit values of other parameters are sin2θ23=0.526+0.032−0.036 and Δm232=2.463+0.071−0.070×10−3 eV2/c4.
Li Z, Abe K, Bronner C, et al., 2018, Measurement of the tau neutrino cross section in atmospheric neutrino oscillations with Super-Kamiokande, PHYSICAL REVIEW D, Vol: 98, ISSN: 2470-0010
Using 5326 days of atmospheric neutrino data, a search for atmospheric tau neutrino appearance has been performed in the Super-Kamiokande experiment. Super-Kamiokande measures the tau normalization to be 1.47±0.32 under the assumption of normal neutrino hierarchy, relative to the expectation of unity with neutrino oscillation. The result excludes the hypothesis of no-tau appearance with a significance level of 4.6σ. The inclusive charged-current tau neutrino cross section averaged by the tau neutrino flux at Super-Kamiokande is measured to be (0.94±0.20)×10−38 cm2. The measurement is consistent with the Standard Model prediction, agreeing to within 1.5σ.
Abe K, Abe K, Ahn SH, et al., 2018, Physics potentials with the second Hyper-Kamiokande detector in Korea, Progress of Theoretical and Experimental Physics, Vol: 2018, ISSN: 2050-3911
Hyper-Kamiokande consists of two identical water-Cherenkov detectors of total 520 kt, with the first one in Japan at 295 km from the J-PARC neutrino beam with 2.5∘ off-axis angles (OAAs), and the second one possibly in Korea at a later stage. Having the second detector in Korea would benefit almost all areas of neutrino oscillation physics, mainly due to longer baselines. There are several candidate sites in Korea with baselines of 1000–1300 km and OAAs of 1∘–3∘.We conducted sensitivity studies on neutrino oscillation physics for a second detector, either in Japan (JD ×2) or Korea (JD + KD), and compared the results with a single detector in Japan. Leptonic charge–parity (CP) symmetry violation sensitivity is improved, especially when the CP is non-maximally violated. The larger matter effect at Korean candidate sites significantly enhances sensitivities to non-standard interactions of neutrinos and mass ordering determination. Current studies indicate the best sensitivity is obtained at Mt. Bisul (1088 km baseline, 1.3∘ OAA). Thanks to a larger (1000 m) overburden than the first detector site, clear improvements to sensitivities for solar and supernova relic neutrino searches are expected.
Kachulis C, Abe K, Bronner C, et al., 2018, Search for boosted dark matter interacting with electrons in super-Kamiokande, Physical Review Letters, Vol: 120, ISSN: 0031-9007
A search for boosted dark matter using 161.9 kt yr of Super-Kamiokande IV data is presented. We search for an excess of elastically scattered electrons above the atmospheric neutrino background, with a visible energy between 100 MeV and 1 TeV, pointing back to the Galactic center or the Sun. No such excess is observed. Limits on boosted dark matter event rates in multiple angular cones around the Galactic center and Sun are calculated. Limits are also calculated for a baseline model of boosted dark matter produced from cold dark matter annihilation or decay. This is the first experimental search for boosted dark matter from the Galactic center or the Sun interacting in a terrestrial detector.
Abe K, Bronner C, Hayato Y, et al., 2018, Search for Neutrinos in Super-Kamiokande Associated with the GW170817 Neutron-star Merger, ASTROPHYSICAL JOURNAL LETTERS, Vol: 857, ISSN: 2041-8205
We report the results of a neutrino search in Super-Kamiokande (SK) for coincident signals with the first detected gravitational wave (GW) produced by a binary neutron-star merger, GW170817, which was followed by a short gamma-ray burst, GRB170817A, and a kilonova/macronova. We searched for coincident neutrino events in the range from 3.5 MeV to ~100 PeV, in a time window ±500 s around the gravitational wave detection time, as well as during a 14-day period after the detection. No significant neutrino signal was observed for either time window. We calculated 90% confidence level upper limits on the neutrino fluence for GW170817. From the upward-going-muon events in the energy region above 1.6 GeV, the neutrino fluence limit is ${16.0}_{-0.6}^{+0.7}$ (${21.3}_{-0.8}^{+1.1}$) cm−2 for muon neutrinos (muon antineutrinos), with an error range of ±5° around the zenith angle of NGC4993, and the energy spectrum is under the assumption of an index of −2. The fluence limit for neutrino energies less than 100 MeV, for which the emission mechanism would be different than for higher-energy neutrinos, is also calculated. It is 6.6 × 107 cm−2 for anti-electron neutrinos under the assumption of a Fermi–Dirac spectrum with average energy of 20 MeV.
Abe K, Bronner C, Haga Y, et al., 2018, Atmospheric neutrino oscillation analysis with external constraints in Super-Kamiokande I-IV, Physical Review D - Particles, Fields, Gravitation and Cosmology, Vol: 97, ISSN: 1550-2368
An analysis of atmospheric neutrino data from all four run periods of Super-Kamiokande optimized for sensitivity to the neutrino mass hierarchy is presented. Confidence intervals for Δm232, sin2θ23, sin2θ13and δCP are presented for normal neutrino mass hierarchy and inverted neutrino mass hierarchy hypotheses, based on atmospheric neutrino data alone. Additional constraints from reactor data on θ13and from published binned T2K data on muon neutrino disappearance and electron neutrino appearance are added to the atmospheric neutrino fit to give enhanced constraints on the above parameters. Over the range of parameters allowed at 90% confidence level, the normal mass hierarchy is favored by between 91.9% and 94.5% based on the combined Super-Kamiokande plus T2K result.
Abe K, Amey J, Andreopoulos C, et al., 2018, Measurement of the single pi(0) production rate in neutral current neutrino interactions on water, Physical Review D - Particles, Fields, Gravitation and Cosmology, Vol: 97, ISSN: 1550-2368
The single π0 production rate in neutral current neutrino interactions on water in a neutrino beam with a peak neutrino energy of 0.6 GeV has been measured using the PØD, one of the subdetectors of the T2K near detector. The production rate was measured for data taking periods when the PØD contained water (2.64 × 1020 protons-on-target) and also periods without water (3.49 × 1020 protons-on-target). A measurement of the neutral current single π0 production rate on water is made using appropriate subtraction of the production rate with water in from the rate with water out of the target region. The subtraction analysis yields 106 ± 41 ± 69 signal events where the uncertainties are statistical (stat.) and systematic (sys.) respectively. This is consistent with the prediction of 157 events from the nominal simulation. The measured to expected ratio is 0.68 ± 0.26 (stat) ± 0.44 (sys) ± 0.12 (flux). The nominal simulation uses a flux integrated cross section of 7.63 × 10−39cm2 per nucleon with an average neutrino interaction energy of 1.3 GeV.
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