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The T2K experiment has observed the disappearance of muon neutrinos from the J-PARC muon-neutrino beam. Using data corresponding to 3.01 × 1020 protons on target, 58 muon neutrino event candidates were observed; 205 ± 17 (syst.) events are expected under the no-oscillation hypothesis. A fit to the observed rate and energy spectrum in a neutrino oscillation framework with three active neutrino flavours in constant density matter, assuming the normal mass hierarchy, yields a best fit mixing angle sin2 θ23 = 0.514 ± 0.082 and best fit mass squared splitting |Δm232| = 2.44+0.17−0.15 × 10-3 eV2 c4, which corresponds to the maximal disappearance probability.

Anomalies observed by different experiments, the most significant ones being the ∼3.8 sigma νe appearance in a ∼50 MeV νµ beam from muon decay at rest observed by the LSND experiment and the ∼3.8 sigma νe and ν ¯ e appearance in a ∼1 GeV neutrino beam from pion decay in flight observed by MiniBooNE, suggest the existence of sterile neutrinos. The Short Baseline Neutrino (SBN) program at Fermilab aims to perform a sensitive search for sterile neutrinos by performing analyses of νe appearance and νµ disappearance employing three Liquid Argon Time Projection Chambers (LAr-TPCs) at different baselines. The VALOR neutrino fitting group was established within the T2K experiment and has led numerous flagship T2K oscillation analyses, and provided sensitivity and detector optimisation studies for DUNE and Hyper-K. The neutrino oscillation framework developed by this group is able to perform fits of several samples and systematic parameters within different neutrino models and experiments. Thus, VALOR is an ideal environment for the neutrino oscillation fits using multiple LAr-TPC detectors with proper treatment of correlated systematic uncertainties necessary for the SBN analyses.

Hyper-Kamiokande is a proposed neutrino physics and proton decay experiment in Japan, due to start operations in 2026. In order to successfully achieve the low-energy (≲10 MeV) physics aims, a dedicated high-efficiency low-energy trigger is required. The test vertices trigger can, for a fixed noise trigger rate, reduce the electron energy trigger threshold by ∼2 MeV, compared with the simple NHITS trigger.

A bstract 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.

Bayesian analysis results require a choice of prior distribution. In long-baseline neutrino oscillation physics, the usual parameterisation of the mixing matrix induces a prior that privileges certain neutrino mass and flavour state symmetries. Here we study the effect of privileging alternate symmetries on the results of the T2K experiment. We find that constraints on the level of CP violation (as given by the Jarlskog invariant) are robust under the choices of prior considered in the analysis. On the other hand, the degree of octant preference for the atmospheric angle depends on which symmetry has been privileged.

The T2K experiment presents new measurements of neutrino oscillation parameters using 19.7 ( 16.3 ) × 10 20 protons on target (POT) in (anti-)neutrino mode at the far detector (FD). Compared to the previous analysis, an additional 4.7 × 10 20 POT neutrino data was collected at the FD. Significant improvements were made to the analysis methodology, with the near-detector analysis introducing new selections and using more than double the data. Additionally, this is the first T2K oscillation analysis to use NA61/SHINE data on a replica of the T2K target to tune the neutrino flux model, and the neutrino interaction model was improved to include new nuclear effects and calculations. Frequentist and Bayesian analyses are presented, including results on sin 2 θ 13 and the impact of priors on the δ CP measurement. Both analyses prefer the normal mass ordering and upper octant of sin 2 θ 23 with a nearly maximally CP-violating phase. Assuming the normal ordering and using the constraint on sin 2 θ 13 from reactors, sin 2 θ 23 = 0 . 561 - 0.032 + 0.021 using Feldman–Cousins corrected intervals, and Δ m 32 2 = 2 . 494 - 0.058 + 0.041 × 10 - 3 eV 2 using constant Δ χ 2 intervals. The CP-violating phase is constrained to δ CP = - 1 . 97 - 0.70 + 0.97 using Feldman–Cousins corrected intervals, and δ CP = 0 , π is excluded at more than 90% confidence level. A Jarlskog invariant of zero is excluded at more than 2 σ credible level using a flat prior in δ CP , and just below 2 σ using a flat prior in sin δ CP . When the external constraint on sin 2 θ 13 is removed, sin 2 θ 13 = 28 . 0 - 6.5 + 2.8 × 10 - 3 , in agreement with measurements from reactor experiments. These results are consistent with previous T2K analyses.

The T2K experiment presents new measurements of neutrino oscillation parameters using protons on target (POT) in (anti-)neutrino mode at the far detector (FD). Compared to the previous analysis, an additional POT neutrino data was collected at the FD. Significant improvements were made to the analysis methodology, with the near-detector analysis introducing new selections and using more than double the data. Additionally, this is the first T2K oscillation analysis to use NA61/SHINE data on a replica of the T2K target to tune the neutrino flux model, and the neutrino interaction model was improved to include new nuclear effects and calculations. Frequentist and Bayesian analyses are presented, including results on and the impact of priors on the measurement. Both analyses prefer the normal mass ordering and upper octant of with a nearly maximally CP-violating phase. Assuming the normal ordering and using the constraint on from reactors, using Feldman-Cousins corrected intervals, and using constant intervals. The CP-violating phase is constrained to using Feldman-Cousins corrected intervals, and is excluded at more than 90% confidence level. A Jarlskog invariant of zero is excluded at more than credible level using a flat prior in and just below using a flat prior in When the external constraint on is removed, in agreement with measurements from reactor experiments. These results are consistent with previous T2K analyses.

The T2K experiment presents new measurements of neutrino oscillation parameters using$$19.7(16.3)\\times 10^{20}$$19.7 ( 16.3 ) × 10 20 protons on target (POT) in (anti-)neutrino mode at the far detector (FD). Compared to the previous analysis, an additional$$4.7\\times 10^{20}$$4.7 × 10 20 POT neutrino data was collected at the FD. Significant improvements were made to the analysis methodology, with the near-detector analysis introducing new selections and using more than double the data. Additionally, this is the first T2K oscillation analysis to use NA61/SHINE data on a replica of the T2K target to tune the neutrino flux model, and the neutrino interaction model was improved to include new nuclear effects and calculations. Frequentist and Bayesian analyses are presented, including results on$$\\sin ^2\\theta _{13}$$sin 2 θ 13 and the impact of priors on the$$\\delta _{\\textrm{CP}}$$δ CP measurement. Both analyses prefer the normal mass ordering and upper octant of$$\\sin ^2\\theta _{23}$$sin 2 θ 23 with a nearly maximally CP-violating phase. Assuming the normal ordering and using the constraint on$$\\sin ^2\\theta _{13}$$sin 2 θ 13 from reactors,$$\\sin ^2\\theta _{23}=0.561^{+0.021}_{-0.032}$$sin 2 θ 23 = 0 . 561 - 0.032 + 0.021 using Feldman–Cousins corrected intervals, and$$\\varDelta {}m^2_{32}=2.494_{-0.058}^{+0.041}\\times 10^{-3}~\\text {eV}^2$$Δ m 32 2 = 2 . 494 - 0.058 + 0.041 × 10 - 3 eV 2 using constant$$\\varDelta \\chi ^{2}$$Δ χ 2 intervals. The CP-violating phase is constrained to$$\\delta _{\\textrm{CP}}=-1.97_{-0.70}^{+0.97}$$δ CP = - 1 . 97 - 0.70 + 0.97 using Feldman–Cousins corrected intervals, and$$\\delta _{\\textrm{CP}}=0,\\pi $$δ CP = 0 , π is excluded at more than 90% confidence level. A Jarlskog invariant of zero is excluded at more than$$2\\sigma $$2 σ credible level using a flat prior in$$\\delta _{\\textrm{CP}},$$δ CP , and just below$$2\\sigma $$2 σ using a flat prior in$$\\sin \\delta _{\\textrm{CP}}.$$sin δ CP . When the external constraint on$$\\sin ^2\\theta _{13}$$sin 2 θ 13 is removed,$$\\sin ^2\\theta _{13}=28.0^{+2.8}_{-6.5}\\times 10^{-3},$$sin 2 θ 13 = 28 . 0 - 6.5 + 2.8 × 10 - 3 , in agreement with measurements from reactor experiments. These results are consistent with previous T2K analyses.

The T2K experiment presents new measurements of neutrino oscillation parameters using $$19.7(16.3)\\times 10^{20}$$ 19.7(16.3)×1020 protons on target (POT) in (anti-)neutrino mode at the far detector (FD). Compared to the previous analysis, an additional $$4.7\\times 10^{20}$$ 4.7×1020 POT neutrino data was collected at the FD. Significant improvements were made to the analysis methodology, with the near-detector analysis introducing new selections and using more than double the data. Additionally, this is the first T2K oscillation analysis to use NA61/SHINE data on a replica of the T2K target to tune the neutrino flux model, and the neutrino interaction model was improved to include new nuclear effects and calculations. Frequentist and Bayesian analyses are presented, including results on $$\\sin ^2\\theta _{13}$$ sin2θ13 and the impact of priors on the $$\\delta _{\\textrm{CP}}$$ δCP measurement. Both analyses prefer the normal mass ordering and upper octant of $$\\sin ^2\\theta _{23}$$ sin2θ23 with a nearly maximally CP-violating phase. Assuming the normal ordering and using the constraint on $$\\sin ^2\\theta _{13}$$ sin2θ13 from reactors, $$\\sin ^2\\theta _{23}=0.561^{+0.021}_{-0.032}$$ sin2θ23=0.561-0.032+0.021 using Feldman–Cousins corrected intervals, and $$\\varDelta {}m^2_{32}=2.494_{-0.058}^{+0.041}\\times 10^{-3}~\\text {eV}^2$$ Δm322=2.494-0.058+0.041×10-3eV2 using constant $$\\varDelta \\chi ^{2}$$ Δχ2 intervals. The CP-violating phase is constrained to $$\\delta _{\\textrm{CP}}=-1.97_{-0.70}^{+0.97}$$ δCP=-1.97-0.70+0.97 using Feldman–Cousins corrected intervals, and $$\\delta _{\\textrm{CP}}=0,\\pi $$ δCP=0,π is excluded at more than 90% confidence level. A Jarlskog invariant of zero is excluded at more than $$2\\sigma $$ 2σ credible level using a flat prior in $$\\delta _{\\textrm{CP}},$$ δCP, and just below $$2\\sigma $$ 2σ using a flat prior in $$\\sin \\delta _{\\textrm{CP}}.$$ sinδCP. When the external constraint on $$\\sin ^2\\theta _{13}$$ sin2θ13 is removed, $$\\sin ^2\\theta _{13}=28.0^{+2.8}_{-6.5}\\times 10^{-3},$$ sin2θ13=28.0-6.5+2.8×10-3, in agreement with measurements from reactor experiments. These results are consistent with previous T2K analyses.

Abstract The T2K experiment presents new measurements of neutrino oscillation parameters using $$19.7(16.3)\\times 10^{20}$$ 19.7 ( 16.3 ) × 10 20 protons on target (POT) in (anti-)neutrino mode at the far detector (FD). Compared to the previous analysis, an additional $$4.7\\times 10^{20}$$ 4.7 × 10 20 POT neutrino data was collected at the FD. Significant improvements were made to the analysis methodology, with the near-detector analysis introducing new selections and using more than double the data. Additionally, this is the first T2K oscillation analysis to use NA61/SHINE data on a replica of the T2K target to tune the neutrino flux model, and the neutrino interaction model was improved to include new nuclear effects and calculations. Frequentist and Bayesian analyses are presented, including results on $$\\sin ^2\\theta _{13}$$ sin 2 θ 13 and the impact of priors on the $$\\delta _{\\textrm{CP}}$$ δ CP measurement. Both analyses prefer the normal mass ordering and upper octant of $$\\sin ^2\\theta _{23}$$ sin 2 θ 23 with a nearly maximally CP-violating phase. Assuming the normal ordering and using the constraint on $$\\sin ^2\\theta _{13}$$ sin 2 θ 13 from reactors, $$\\sin ^2\\theta _{23}=0.561^{+0.021}_{-0.032}$$ sin 2 θ 23 = 0 . 561 - 0.032 + 0.021 using Feldman–Cousins corrected intervals, and $$\\varDelta {}m^2_{32}=2.494_{-0.058}^{+0.041}\\times 10^{-3}~\\text {eV}^2$$ Δ m 32 2 = 2 . 494 - 0.058 + 0.041 × 10 - 3 eV 2 using constant $$\\varDelta \\chi ^{2}$$ Δ χ 2 intervals. The CP-violating phase is constrained to $$\\delta _{\\textrm{CP}}=-1.97_{-0.70}^{+0.97}$$ δ CP = - 1 . 97 - 0.70 + 0.97 using Feldman–Cousins corrected intervals, and $$\\delta _{\\textrm{CP}}=0,\\pi $$ δ CP = 0 , π is excluded at more than 90% confidence level. A Jarlskog invariant of zero is excluded at more than $$2\\sigma $$ 2 σ credible level using a flat prior in $$\\delta _{\\textrm{CP}},$$ δ CP , and just below $$2\\sigma $$ 2 σ using a flat prior in $$\\sin \\delta _{\\textrm{CP}}.$$ sin δ CP . When the external constraint on $$\\sin ^2\\theta _{13}$$ sin 2 θ 13 is removed, $$\\sin ^2\\theta _{13}=28.0^{+2.8}_{-6.5}\\times 10^{-3},$$ sin 2 θ 13 = 28 . 0 - 6.5 + 2.8 × 10 - 3 , in agreement with measurements from reactor experiments. These results are consistent with previous T2K analyses.