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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)×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.

Abstract 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 $\\mu^\\pm$ 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, $p_{\\mu}>400~{\\rm MeV}/c$ and $\\theta_{\\mu}<30^{\\circ}$, in the laboratory frame. An absence of pions and protons in the detectable phase spaces of $p_{\\pi}>200~{\\rm MeV}/c$, $\\theta_{\\pi}<70^{\\circ}$ and $p_{\\rm p}>600~{\\rm MeV}/c$, $\\theta_{\\rm p}<70^{\\circ}$ is required. In this paper, both the $\\overline{\\nu}_\\mu$ cross-sections and $\\overline{\\nu}_\\mu+\\nu_\\mu$ cross-sections on water and hydrocarbon targets and their ratios are provided by using the D’Agostini unfolding method. The results of the integrated $\\overline{\\nu}_\\mu$ cross-section measurements over this phase space are $\\sigma_{\\rm H_{2}O}=(1.082\\pm0.068(\\rm stat.)^{+0.145}_{-0.128}(\\rm syst.)) \\times 10^{-39}\\,{\\rm cm^{2} / nucleon}$, $\\sigma_{\\rm CH}=(1.096\\pm0.054(\\rm stat.)^{+0.132}_{-0.117}(\\rm syst.)) \\times 10^{-39}\\,{\\rm cm^{2} / nucleon}$, and $\\sigma_{\\rm H_{2}O}/\\sigma_{\\rm CH} = 0.987\\pm0.078(\\rm stat.)^{+0.093}_{-0.090}(\\rm syst.)$. The $\\overline{\\nu}_\\mu+\\nu_\\mu$ cross-section is $\\sigma_{\\rm H_{2}O} = (1.155\\pm0.064(\\rm stat.)^{+0.148}_{-0.129}(\\rm syst.)) \\times 10^{-39}\\,{\\rm cm^{2} / nucleon}$, $\\sigma_{\\rm CH}=(1.159\\pm0.049(\\rm stat.)^{+0.129}_{-0.115}(\\rm syst.)) \\times 10^{-39}\\,{\\rm cm^{2} / nucleon}$, and $\\sigma_{\\rm H_{2}O}/\\sigma_{\\rm CH}=0.996\\pm0.069(\\rm stat.)^{+0.083}_{-0.078}(\\rm syst.)$.

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$\\mu^\\pm$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,$p_{\\mu}>400~{\\rm MeV}/c$and$\\theta_{\\mu}<30^{\\circ}$ , in the laboratory frame. An absence of pions and protons in the detectable phase spaces of$p_{\\pi}>200~{\\rm MeV}/c$ ,$\\theta_{\\pi}<70^{\\circ}$and$p_{\\rm p}>600~{\\rm MeV}/c$ ,$\\theta_{\\rm p}<70^{\\circ}$is required. In this paper, both the$\\overline{\\nu}_\\mu$cross-sections and$\\overline{\\nu}_\\mu+\\nu_\\mu$cross-sections on water and hydrocarbon targets and their ratios are provided by using the D’Agostini unfolding method. The results of the integrated$\\overline{\\nu}_\\mu$cross-section measurements over this phase space are$\\sigma_{\\rm H_{2}O}=(1.082\\pm0.068(\\rm stat.)^{+0.145}_{-0.128}(\\rm syst.)) \\times 10^{-39}\\,{\\rm cm^{2} / nucleon}$ ,$\\sigma_{\\rm CH}=(1.096\\pm0.054(\\rm stat.)^{+0.132}_{-0.117}(\\rm syst.)) \\times 10^{-39}\\,{\\rm cm^{2} / nucleon}$ , and$\\sigma_{\\rm H_{2}O}/\\sigma_{\\rm CH} = 0.987\\pm0.078(\\rm stat.)^{+0.093}_{-0.090}(\\rm syst.)$ . The$\\overline{\\nu}_\\mu+\\nu_\\mu$cross-section is$\\sigma_{\\rm H_{2}O} = (1.155\\pm0.064(\\rm stat.)^{+0.148}_{-0.129}(\\rm syst.)) \\times 10^{-39}\\,{\\rm cm^{2} / nucleon}$ ,$\\sigma_{\\rm CH}=(1.159\\pm0.049(\\rm stat.)^{+0.129}_{-0.115}(\\rm syst.)) \\times 10^{-39}\\,{\\rm cm^{2} / nucleon}$ , and$\\sigma_{\\rm H_{2}O}/\\sigma_{\\rm CH}=0.996\\pm0.069(\\rm stat.)^{+0.083}_{-0.078}(\\rm syst.)$ .

This paper reports the first measurement of muon neutrino charged-current interactions without pions in the final state using multiple detectors with correlated energy spectra at T2K. The data was collected on hydrocarbon targets using the off-axis T2K near detector (ND280) and the on-axis T2K near detector (INGRID) with neutrino energy spectra peaked at 0.6 GeV and 1.1 GeV respectively. The correlated neutrino flux presents an opportunity to reduce the impact of the flux uncertainty and to study the energy dependence of neutrino interactions. The extracted double-differential cross sections are compared to several Monte Carlo neutrino-nucleus interaction event generators showing the agreement between both detectors individually and with the correlated result.

The current laws of physics do not explain the observed imbalance of matter and antimatter in the universe. Sakharov proposed that an explanation would require the violation of CP symmetry between matter and antimatter. The only CP violation observed so far is in the weak interactions of quarks, and it is too small to explain the matter-antimatter imbalance of the universe. It has been shown that CP violation in the lepton sector could generate the matter-antimatter disparity through the process called leptogenesis. The quantum mixing of neutrinos, the neutral leptons in the Standard Model, provides a potential source of CP violation through a complex phase dCP, which may have consequences for theoretical models of leptogenesis. This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible with accelerator-produced beams as established by the T2K experiment. Until now, the value of dCP has not been significantly constrained by neutrino oscillation experiments. Here the T2K collaboration reports a measurement that favors large enhancement of the neutrino oscillation probability, excluding values of dCP which result in a large enhancement of the observed anti-neutrino oscillation probability at three standard deviations (3 sigma). The 3 sigma confidence level interval for dCP, which is cyclic and repeats every 2pi, is [-3.41,-0.03] for the so-called normal mass ordering, and [-2.54,-0.32] for the inverted mass ordering. Our results show an indication of CP violation in the lepton sector. Herein we establish methods for sensitive searches for matter-antimatter asymmetry in neutrino oscillations using accelerator-produced neutrino beams. Future measurements with larger data samples will determine whether the leptonic CP violation is larger than the quark sector CP violation.

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, \\(d\\sigma/dp\\) and \\(d\\sigma/d\\cos(\\theta)\\), and the total cross-sections in a limited phase-space in momentum and scattering angle (\\(p > 300\\) MeV/c and \\(\\theta \\leq 45^{\\circ}\\)) are measured using a binned maximum likelihood fit and compared to the neutrino Monte Carlo generator predictions, resulting in good agreement.

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.

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\\(\\times\\)10\\(^{20}\\) and 6.3\\(\\times\\)10\\(^{20}\\) 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.