284 results found
Matsumoto R, Abe K, Hayato Y, et al., 2022, Search for proton decay via p →μ+K0 in 0.37 megaton-years exposure of Super-Kamiokande, Physical Review D, Vol: 106, ISSN: 2470-0010
We searched for proton decay via p→μ+K0 in 0.37 Mton·years of data collected between 1996 and 2018 from the Super-Kamiokande water Cherenkov experiment. The selection criteria were defined separately for KS0 and KL0 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·years of exposure and uses an improved event reconstruction, we set a lower limit of 3.6×1033 years on the proton lifetime.
Abe K, Bronner C, Hayato Y, et al., 2022, Search for solar electron anti-neutrinos due to spin-flavor precession in the Sun with Super-Kamiokande-IV, Astroparticle Physics, Vol: 139, ISSN: 0927-6505
Due to a very low production rate of electron anti-neutrinos (ν̄e) via nuclear fusion in the Sun, a flux of solar ν̄e is unexpected. An appearance of ν̄e in solar neutrino flux opens a new window for the new physics beyond the standard model. In particular, a spin-flavor precession process is expected to convert an electron neutrino into an electron anti-neutrino (νe→ν̄e) when neutrino has a finite magnetic moment. In this work, we have searched for solar ν̄e in the Super-Kamiokande experiment, using neutron tagging to identify their inverse beta decay signature. We identified 78 ν̄e candidates for neutrino energies of 9.3 to 17.3 MeV in 2970.1 live days with a fiducial volume of 22.5 kiloton water (183.0 kton⋅year exposure). The energy spectrum has been consistent with background predictions and we thus derived a 90% confidence level upper limit of 4.7×10−4 on the νe→ν̄e conversion probability in the Sun. We used this result to evaluate the sensitivity of future experiments, notably the Super-Kamiokande Gadolinium (SK-Gd) upgrade.
Edmonds A, Quirk J, Wong M-L, et al., 2022, Measurement of proton, deuteron, triton, and alpha particle emission after nuclear muon capture on Al, Si, and Ti with the AlCap experiment, Physical Review C: Nuclear Physics, Vol: 105, Pages: 1-21, ISSN: 0556-2813
Background: Heavy charged particles after nuclear muon capture are an important nuclear physics background to the muon-to-electron conversion experiments Mu2e and COMET, which will search for charged lepton flavor violation at an unprecedented level of sensitivity.Purpose: The AlCap experiment aimed to measure the yield and energy spectra of protons, deuterons, tritons, and α particles emitted after the nuclear capture of muons stopped in Al, Si, and Ti in the low-energy range relevant for the muon-to-electron conversion experiments.Methods: Individual charged particle types were identified in layered silicon detector packages and their initial energy distributions were unfolded from the observed energy spectra.Results: The proton yields per muon capture were determined as Yp(Al)=26.64(28stat.)(77syst.)×10−3 and Yp(Ti)=26.48(35)(80)×10−3 in the energy range 3.5–20.0 MeV, and as Yp(Si)=52.5(6)(18)×10−3 in the energy range 4.0–20.0 MeV. Detailed information on yields and energy spectra for all observed nuclei are presented in the paper.Conclusions: The yields in the candidate muon stopping targets, Al and Ti, are approximately half of that in Si, which was used in the past to estimate this background. The reduced background allows for less shielding and a better energy resolution in these experiments. It is anticipated that the comprehensive information presented in this paper will stimulate modern theoretical calculations of the rare process of muon capture with charged particle emission and inform the design of future muon-to-electron conversion experiments.
Abe K, Bronner C, Hayato Y, et al., 2022, First gadolinium loading to Super-Kamiokande, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, Vol: 1027, ISSN: 0168-9002
Abe K, Bronner C, Hayato Y, et al., 2021, Diffuse supernova neutrino background search at Super-Kamiokande, PHYSICAL REVIEW D, Vol: 104, ISSN: 2470-0010
Abe K, Bronner C, Hayato Y, et al., 2021, Search for Neutrinos in Coincidence with Gravitational Wave Events from the LIGO-Virgo O3a Observing Run with the Super-Kamiokande Detector, ASTROPHYSICAL JOURNAL, Vol: 918, ISSN: 0004-637X
Abe K, Bronner C, Hayato Y, et al., 2021, Search for tens of MeV neutrinos associated with gamma-ray bursts in Super-Kamiokande, PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS, Vol: 2021, ISSN: 2050-3911
Abe K, Adrich P, Aihara H, et al., 2021, Supernova Model Discrimination with Hyper-Kamiokande, ASTROPHYSICAL JOURNAL, Vol: 916, ISSN: 0004-637X
Abe K, Akhlaq N, Akutsu R, et al., 2021, First T2K measurement of transverse kinematic imbalance in the muon-neutrino charged-current single-π+ production channel containing at least one proton, Physical Review D, Vol: 103, Pages: 1-27, ISSN: 2470-0010
This paper reports the first T2K measurement of the transverse kinematic imbalance in the single-π+ production channel of neutrino interactions. We measure the differential cross sections in the muon-neutrino charged-current interaction on hydrocarbon with a single π+ and at least one proton in the final state, at the ND280 off axis near detector of the T2K experiment. The extracted cross sections are compared to the predictions from different neutrino-nucleus interaction event generators. Overall, the results show a preference for models that have a more realistic treatment of nuclear medium effects including the initial nuclear state and final-state interactions.
Abe K, Akhlaq N, Akutsu R, et al., 2021, Improved constraints on neutrino mixing from the T2K experiment with 3.13×1021 protons on target, Physical Review D, Vol: 103, Pages: 1-59, ISSN: 2470-0010
The T2K experiment reports updated measurements of neutrino and antineutrino oscillations using both appearance and disappearance channels. This result comes from an exposure of 14.9(16.4)×1020 protons on target in neutrino (antineutrino) mode. Significant improvements have been made to the neutrino interaction model and far detector reconstruction. An extensive set of simulated data studies have also been performed to quantify the effect interaction model uncertainties have on the T2K oscillation parameter sensitivity. T2K performs multiple oscillation analyses that present both frequentist and Bayesian intervals for the Pontecorvo-Maki-Nakagawa-Sakata parameters. For fits including a constraint on sin2θ13 from reactor data and assuming normal mass ordering T2K measures sin2θ23=0.53+0.03−0.04 and Δm232=(2.45±0.07)×10−3 eV2 c−4. The Bayesian analyses show a weak preference for normal mass ordering (89% posterior probability) and the upper sin2θ23 octant (80% posterior probability), with a uniform prior probability assumed in both cases. The T2K data exclude CP conservation in neutrino oscillations at the 2σ level.
Abe K, Akhlaq N, Akutsu R, et al., 2021, Measurements of (nu)over-bar(mu) and (nu)over-bar(mu) + nu(mu) charged-current cross-sections without detected pions or protons on water and hydrocarbon at a mean anti-neutrino energy of 0.86 GeV, Progress of Theoretical and Experimental Physics, Vol: 2021, ISSN: 0033-068X
We report measurements of the flux-integrated ν̅μ and ν̅μ + νμ charged-current cross-sections on water and hydrocarbon targets using the T2K anti-neutrino beam with a mean beam energy of 0.86 GeV. The signal is defined as the (anti-)neutrino charged-current interaction with one induced μ± and no detected charged pion or proton. These measurements are performed using a new WAGASCI module recently added to the T2K setup in combination with the INGRID Proton Module. The phase space of muons is restricted to the high-detection efficiency region, pμ>400 MeV/c and θμ<30∘, in the laboratory frame. An absence of pions and protons in the detectable phase spaces of pπ>200 MeV/c, θπ<70∘ and pp>600 MeV/c, θp<70∘ is required. In this paper, both the ν¯¯¯μ cross-sections and ν¯¯¯μ+νμ cross-sections on water and hydrocarbon targets and their ratios are provided by using the D’Agostini unfolding method. The results of the integrated ν¯¯¯μ cross-section measurements over this phase space are σH2O=(1.082±0.068(stat.)+0.145−0.128(syst.))×10−39cm2/nucleon, σCH=(1.096±0.054(stat.)+0.132−0.117(syst.))×10−39cm2/nucleon, and σH2O/σCH=0.987±0.078(stat.)+0.093−0.090(syst.). The ν¯¯¯μ+νμ cross-section is σH2O=(1.155±0.064(stat.)+0.148−0.129(syst.))×10−39cm2/nucleon, σCH=(1.159±0.049(stat.)+0.129−0.115(syst.))×10−39cm2/nucleon, and σH2O/σCH=0.996±0.069(stat.)+0.083−0.078(syst.).
Abe K, Akhlaq N, Akutsu R, et al., 2021, T2K measurements of muon neutrino and antineutrino disappearance using 3.13 x 10(21) protons on target, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 103, Pages: 1-9, ISSN: 1550-2368
We report measurements by the T2K experiment of the parameters θ23 and Δm232, which govern the disappearance of muon neutrinos and antineutrinos in the three-flavor PMNS neutrino oscillation model at T2K’s neutrino energy and propagation distance. Utilizing the ability of the experiment to run with either a mainly neutrino or a mainly antineutrino beam, muon-like events from each beam mode are used to measure these parameters separately for neutrino and antineutrino oscillations. Data taken from 1.49×1021 protons on target (POT) in neutrino mode and 1.64×1021 POT in antineutrino mode are used. The best-fit values obtained by T2K were sin2(θ23)=0.51+0.06−0.07(0.43+0.21−0.05) and Δm232=2.47+0.08−0.09(2.50+0.18−0.13)×10−3 eV2/c4 for neutrinos (antineutrinos). No significant differences between the values of the parameters describing the disappearance of muon neutrinos and antineutrinos were observed. An analysis using an effective two-flavor neutrino oscillation model where the sine of the mixing angle is allowed to take nonphysical values larger than 1 is also performed to check the consistency of our data with the three-flavor model. Our data were found to be consistent with a physical value for the mixing angle.
Abe K, Bronner C, Hayato Y, et al., 2021, Neutron-antineutron oscillation search using a 0.37 megaton-years exposure of Super-Kamiokande, PHYSICAL REVIEW D, Vol: 103, ISSN: 2470-0010
Takenaka A, Abe K, Bronner C, et al., 2020, Search for proton decay via p -> e(+)pi(0) and p -> mu(+)pi(0) with an enlarged fiducial volume in Super-Kamiokande I-IV, PHYSICAL REVIEW D, Vol: 102, ISSN: 2470-0010
Blondel A, Bogomilov M, Bordoni S, et al., 2020, The SuperFGD Prototype charged particle beam tests, JOURNAL OF INSTRUMENTATION, Vol: 15, ISSN: 1748-0221
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.
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.
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