Publications
52 results found
Harada M, Abe K, Bronner C, et al., 2023, Search for Astrophysical Electron Antineutrinos in Super-Kamiokande with 0.01% Gadolinium-loaded Water, ASTROPHYSICAL JOURNAL LETTERS, Vol: 951, ISSN: 2041-8205
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Abe K, Akhlaq N, Akutsu R, et al., 2022, Scintillator ageing of the T2K near detectors fro 2010 to 2021, Journal of Instrumentation, Vol: 17, Pages: 1-36, ISSN: 1748-0221
The T2K experiment widely uses plastic scintillator as a target for neutrino interactions and an active medium for the measurement of charged particles produced in neutrino interactions at its near detector complex. Over 10 years of operation the measured light yield recorded by the scintillator based subsystems has been observed to degrade by 0.9–2.2% per year. Extrapolation of the degradation rate through to 2040 indicates the recorded light yield should remain above the lower threshold used by the current reconstruction algorithms for all subsystems. This will allow the near detectors to continue contributing to important physics measurements during the T2K-II and Hyper-Kamiokande eras. Additionally, work to disentangle the degradation of the plastic scintillator and wavelength shifting fibres shows that the reduction in light yield can be attributed to the ageing of the plastic scintillator. The long component of the attenuation length of the wavelength shifting fibres was observed to degrade by 1.3–5.4% per year, while the short component of the attenuation length did not show any conclusive degradation.
Matsumoto R, Abe K, Hayato Y, et al., 2022, Search for proton decay via p -> mu(+) K-0 in 0.37 megaton-years exposure of Super-Kamiokande, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 106, Pages: 1-13, ISSN: 1550-2368
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 K0S and K0L 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.
Machado LN, Abe K, Hayato Y, et al., 2022, Pre-supernova alert system for super-kamiokande, The Astrophysical Journal: an international review of astronomy and astronomical physics, Vol: 935, Pages: 1-14, ISSN: 0004-637X
In 2020, the Super-Kamiokande (SK) experiment moved to a new stage (SK-Gd) in which gadolinium (Gd) sulfate octahydrate was added to the water in the detector, enhancing the efficiency to detect thermal neutrons and consequently improving the sensitivity to low energy electron anti-neutrinos from inverse beta decay (IBD) interactions. SK-Gd has the potential to provide early alerts of incipient core-collapse supernovae through detection of electron anti-neutrinos from thermal and nuclear processes responsible for the cooling of massive stars before the gravitational collapse of their cores. These pre-supernova neutrinos emitted during the silicon burning phase can exceed the energy threshold for IBD reactions. We present the sensitivity of SK-Gd to pre-supernova stars and the techniques used for the development of a pre-supernova alarm based on the detection of these neutrinos in SK, as well as prospects for future SK-Gd phases with higher concentrations of Gd. For the current SK-Gd phase, high-confidence alerts for Betelgeuse could be issued up to 9 hr in advance of the core collapse itself.
Abe K, Bronner C, Hayato Y, et al., 2022, First gadolinium loading to Super-Kamiokande, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment, Vol: 1027, Pages: 1-15, ISSN: 0168-9002
In order to improve Super-Kamiokande’s neutron detection efficiency and to thereby increase its sensitivity tothe diffuse supernova neutrino background flux, 13 tons of Gd2(SO4)3⋅ 8H2O (gadolinium sulfate octahydrate)was dissolved into the detector’s otherwise ultrapure water from July 14 to August 17, 2020, marking thestart of the SK-Gd phase of operations. During the loading, water was continuously recirculated at a rate of 60m3/h, extracting water from the top of the detector and mixing it with concentrated Gd2(SO4)3⋅ 8H2O solutionto create a 0.02% solution of the Gd compound before injecting it into the bottom of the detector. A clearboundary between the Gd-loaded and pure water was maintained through the loading, enabling monitoring ofthe loading itself and the spatial uniformity of the Gd concentration over the 35 days it took to reach the top ofthe detector. During the subsequent commissioning the recirculation rate was increased to 120 m3/h, resultingin a constant and uniform distribution of Gd throughout the detector and water transparency equivalent tothat of previous pure-water operation periods. Using an Am–Be neutron calibration source the mean neutroncapture time was measured to be 115 ± 1 μs, which corresponds to a Gd concentration of 111 ± 2 ppm, asexpected for this level of Gd loading. This paper describes changes made to the water circulation system for this detector upgrade, the Gd loading procedure, detector commissioning, and the first neutron calibrationmeasurements in SK-Gd.
Abe K, Bronner C, Hayato Y, et al., 2021, Diffuse supernova neutrino background search at Super-Kamiokande, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 104, Pages: 1-41, ISSN: 1550-2368
y, potentialities of the gadolinium phase of SK and the future Hyper-Kamiokande experiment are discussed.
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, 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, 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, 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
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, 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.
Scott M, 2019, Oscillation analysis with NuPRISM, 27th International Conference on Neutrino Physics and Astrophysics (Neutrino), Publisher: IOP PUBLISHING LTD, Pages: 1-3, ISSN: 1742-6588
NuPRISM is a proposed intermediate water Cherenkov detector for the T2K and Hyper-K long baseline neutrino oscillation experiments. The detector makes use of the off-axis effect, where the peak energy of the neutrino flux falls with increasing perpendicular distance from the neutrino beam axis. By spanning the 1 – 4 degree off-axis angular range NuPRISM can sample neutrino fluxes with peak energies from 1200 to 400 MeV respectively. These samples can be linearly combined to create an effective neutrino flux, such as the muon neutrino flux at the far detector for some choice of the neutrino oscillation parameters.This proceedings presents the NuPRISM muon neutrino disappearance analysis, showing that this technique is unaffected by mis-modelled neutrino cross-sections. It also presents the electron neutrino appearance analysis, showing the preliminary uncertainty on a measurement of the ${{{\nu _e}} \over {{\nu _\mu }}}$ cross-section ratio at NuPRISM.
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.
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.
Dell'Acqua A, Aduszkiewicz A, Ahlers M, et al., 2018, Future Opportunities in Accelerator-based Neutrino Physics
This document summarizes the conclusions of the Neutrino Town Meeting held atCERN in October 2018 to review the neutrino field at large with the aim ofdefining a strategy for accelerator-based neutrino physics in Europe. Theimportance of the field across its many complementary components is stressed.Recommendations are presented regarding the accelerator based neutrino physics,pertinent to the European Strategy for Particle Physics. We address inparticular i) the role of CERN and its neutrino platform, ii) the importance ofancillary neutrino cross-section experiments, and iii) the capability of fixedtarget experiments as well as present and future high energy colliders tosearch for the possible manifestations of neutrino mass generation mechanisms.
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.
Abe K, Amey J, Andreopoulos C, et al., 2018, Characterization of nuclear effects in muon-neutrino scattering on hydrocarbon with a measurement of final-state kinematics and correlations in charged-current pionless interactions at T2K, PHYSICAL REVIEW D, Vol: 98, ISSN: 2470-0010
This paper reports measurements of final-state proton multiplicity, muon and proton kinematics, and their correlations in charged-current pionless neutrino interactions, measured by the T2K ND280 near detector in its plastic scintillator (C8H8) target. The data were taken between years 2010 and 2013, corresponding to approximately 6×1020 protons on target. Thanks to their exploration of the proton kinematics and of imbalances between the proton and muon kinematics, the results offer a novel probe of the nuclear-medium effects most pertinent to the (sub-)GeV neutrino-nucleus interactions that are used in accelerator-based long-baseline neutrino oscillation measurements. These results are compared to many neutrino-nucleus interaction models which all fail to describe at least part of the observed phase space. In case of events without a proton above a detection threshold in the final state, a fully consistent implementation of the local Fermi gas model with multinucleon interactions gives the best description of the data. In the case of at least one proton in the final state, the spectral function model agrees well with the data, most notably when measuring the kinematic imbalance between the muon and the proton in the plane transverse to the incoming neutrino. Within the models considered, only the existence of multinucleon interactions are able to describe the extracted cross section within regions of high transverse kinematic imbalance. The effect of final-state interactions is also discussed.
Abe K, Amey J, Andreopoulos C, et al., 2018, Measurement of inclusive double-differential nu(mu) charged-current cross section with improved acceptance in the T2K off-axis near detector, Physical Review D - Particles, Fields, Gravitation and Cosmology, Vol: 98, ISSN: 1550-2368
We report a measurement of the flux-integrated cross section for inclusive muon neutrino charged-current interactions on carbon. The double-differential measurements are given as a function of the muon momentum and angle. Relative to our previous publication on this topic, these results have an increased angular acceptance and higher statistics. The data sample presented here corresponds to 5.7×1020 protons on target. The total flux-integrated cross section is measured to be (6.950±0.662)×10−39 cm2 nucleon−1 and is consistent with our simulation.
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.
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.
Abe K, Amey J, Andreopoulos C, et al., 2018, First measurement of the nu(mu) charged-current cross section on a water target without pions in the final state, Physical Review D - Particles, Fields, Gravitation and Cosmology, Vol: 97, ISSN: 1550-2368
This paper reports the first differential measurement of the charged-current interaction cross section of νμ on water with no pions in the final state. This flux-averaged measurement has been made using the T2K experiment’s off-axis near detector, and is reported in doubly differential bins of muon momentum and angle. The flux-averaged total cross section in a restricted region of phase space was found to be σ = (0.95 ± 0.08 (stat) ± 0.06 (det syst) ± 0.04 (model syst) ± 0.08 (flux)) × 10 − 38cm2/n.
Abe K, Amey J, Andreopoulos C, et al., 2017, Measurement of neutrino and antineutrino oscillations by the T2K experiment including a new additional sample of nu(e) interactions at the far detector, Physical Review D - Particles, Fields, Gravitation and Cosmology, Vol: 96, ISSN: 1550-2368
The T2K experiment reports an updated analysis of neutrino and antineutrino oscillations in appearanceand disappearance channels. A sample of electron neutrino candidates at Super-Kamiokande in which a piondecay has been tagged is added to the four single-ring samples used in previous T2K oscillation analyses.Through combined analyses of these five samples, simultaneous measurements of four oscillationparameters, jΔm232j, sin2 θ23, sin2 θ13, and δCP and of the mass ordering are made. A set of studies ofsimulated data indicates that the sensitivity to the oscillation parameters is not limited by neutrino interactionmodel uncertainty. Multiple oscillation analyses are performed, and frequentist and Bayesian intervals arepresented for combinations of the oscillation parameters with and without the inclusion of reactor constraintson sin2 θ13. When combined with reactor measurements, the hypothesis of CP conservation (δCP ¼ 0 or π) isexcluded at 90% confidence level. The 90% confidence region for δCP is½−2.95;−0.44 (½−1.47;−1.27) fornormal (inverted) ordering. The central values and 68% confidence intervals for the other oscillationparameters for normal (inverted) ordering are Δm232 ¼ 2.54 0.08ð2.51 0.08Þ × 10−3 eV2=c4 andsin2θ23 ¼ 0.55þ0.05 −0.09 (0.55þ0.05 −0.08 ), compatible with maximal mixing. In the Bayesian analysis, the dataweakly prefer normal ordering (Bayes factor 3.7) and the upper octant for sin2 θ23 (Bayes factor 2.4).
Abe K, Amey J, Andreopoulos C, et al., 2017, Updated T2K measurements of muon neutrino and antineutrino disappearance using 1.5 x 10(21) protons on target, PHYSICAL REVIEW D, Vol: 96, ISSN: 2470-0010
We report measurements by the T2K experiment of the parameters θ23 and Δm232 governing the disappearance of muon neutrinos and antineutrinos in the three-flavor neutrino oscillation model. Utilizing the ability of the experiment to run with either a mainly neutrino or a mainly antineutrino beam, the parameters are measured separately for neutrinos and antineutrinos. Using 7.482×1020 POT in neutrino running mode and 7.471×1020 POT in antineutrino mode, T2K obtained sin2(θ23)=0.51+0.08−0.07and Δm232=2.53+0.15−0.13×10−3 eV2/c4 for neutrinos, and sin2(¯θ23)=0.42+0.25−0.07 and Δ¯m232=2.55+0.33−0.27×10−3 eV2/c4 for antineutrinos (assuming normal mass ordering). No significant differences between the values of the parameters describing the disappearance of muon neutrinos and antineutrinos were observed.
Abe K, Amey J, Andreopoulos C, et al., 2017, Search for Lorentz and CPT violation using sidereal time dependence of neutrino flavor transitions over a short baseline, Physical Review D, Vol: 95, ISSN: 2470-0010
A class of extensions of the Standard Model allows Lorentz and CPT violations, which can be identified by the observation of sidereal modulations in the neutrino interaction rate. A search for such modulations was performed using the T2K on-axis near detector. Two complementary methods were used in this study, both of which resulted in no evidence of a signal. Limits on associated Lorentz and CPT-violating terms from the Standard Model extension have been derived by taking into account their correlations in this model for the first time. These results imply such symmetry violations are suppressed by a factor of more than 1020 at the GeV scale.
Abe K, Amey J, Andreopoulos C, et al., 2017, Combined analysis of neutrino and antineutrino oscillations at T2K, Physical Review Letters, Vol: 118, ISSN: 0031-9007
T2K reports its first results in the search for CP violation in neutrino oscillations using appearance and disappearance channels for neutrino- and antineutrino-mode beams. The data include all runs from January 2010 to May 2016 and comprise 7.482×1020 protons on target in neutrino mode, which yielded in the far detector 32 e-like and 135 μ-like events, and 7.471×1020 protons on target in antineutrino mode, which yielded 4 e-like and 66 μ-like events. Reactor measurements of sin22θ13 have been used as an additional constraint. The one-dimensional confidence interval at 90% for the phase δCP spans the range (−3.13, −0.39) for normal mass ordering. The CP conservation hypothesis (δCP=0, π) is excluded at 90% C.L.
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