The Super-Kamiokande and T2K Collaborations present a joint measurement of neutrino oscillation parameters from their atmospheric and beam neutrino data. It uses a common interaction model for events overlapping in neutrino energy and correlated detector systematic uncertainties between the two datasets, which are found to be compatible. Using 3244.4 days of atmospheric data and a beam exposure of 19.7(16.3)×1020 protons on target in (anti)neutrino mode, the analysis finds a 1.9σ exclusion of CP conservation (defined as JCP=0) and a 1.2σ exclusion of the inverted mass ordering. Published by the American Physical Society 2025

In this work, the Coulomb effects (Coulomb correlations) in pi+pi- pairs produced in p + Ni collisions at 24 GeV=c, are studied using experimental pi+pi- pair distributions in Q, the relative momentum in the pair center-of-mass system (c.m.s.), and its projections Q(L) (longitudinal component) and Q(t) (transverse component) relative to the pair direction in the laboratory system (LS). The major part of the pion pairs ("Coulomb pairs") is produced in the decay of rho, omega and Delta resonances and other short-lived sources. In these pairs, the significant Coulomb interaction occurs at small Q, dominating the pi+pi- interaction in the final state. The minor part of the pairs ("non-Coulomb pairs") is produced if one or both pions arose from long-lived sources like eta, eta ' or from different interactions. In this case, the final state interaction is practically absent. The Q, Q(L), and Q(t) distributions of the Coulomb pairs in the c.m.s. have been simulated assuming they are described by the phase space modified by the known point-like Coulomb correlation function A(C)(Q), corrected for small effects due to the nonpointlike pair production and the strong two-pion interaction. The same distributions of non-Coulomb pairs have been simulated according to the phase space, but without A(C)(Q). In all Q(t) intervals, the experimental Q(L) spectrum shows a peak around Q(L) = 0 caused by the Coulomb final state interaction. The full width at half maximum increases with Q(t) from 3 MeV/c for 0 < Q(t) < 0.25 MeV/c to 11 MeV/c for 4.0 < Q(t) < 5.0 MeV/c. The experimental Q(L) distributions have been fitted with two free parameters: the fraction of Coulomb pairs and the normalization constant. The precision of the description of these distributions is better than 2% in Q(t) intervals 2-3, 3-4, and 4-5 MeV/c and better than 0.5% in the total Q(t) interval 0-5 MeV/c. It is shown that the number of Coulomb pairs in all Q(t) intervals, including the small Q(t) (small opening angles theta in the LS) is calculated with theoretical precision better than 2%. The comparison of the simulated and experimental numbers of Coulomb pairs at small Q(t) allows us to check and correct the detection efficiency for the pairs with small. (0.06 mrad and smaller). It is shown that Coulomb pairs can be used as a new physical tool to check and correct the quality of the simulated events. The special property of the Coulomb pairs is the possibility of checking and correcting the detection efficiency, especially for the pairs with small opening angles.

We report an updated measurement of the $\nu_{\mu}$-induced, and the first measurement of the $\bar{\nu}_{\mu}$-induced coherent charged pion production cross section on $^{12}C$ nuclei in the T2K experiment. This is measured in a restricted region of the final-state phase space for which $p_{\mu,\pi}>0.2$ GeV, $\cos(\theta_{\mu})>0.8$ and $\cos(\theta_{\pi})>0.6$, and at a mean (anti)neutrino energy of 0.85 GeV using the T2K near detector. The measured $\nu_{\mu}$ CC coherent pion production flux-averaged cross section on $^{12}C$ is $(2.98 \pm 0.37 (stat.) \pm 0.31 (syst.) \substack{ +0.49 \\ -0.00 } \mathrm{ (Q^2\,model)}) \times 10^{-40}~\mathrm{cm}^{2}$. The new measurement of the $\bar{\nu}_{\mu}$-induced cross section on $^{12}{C}$ is $(3.05 \pm 0.71 (stat.) \pm 0.39 (syst.) \substack{ +0.74 \\ -0.00 } \mathrm{(Q^2\,model)}) \times 10^{-40}~\mathrm{cm}^{2}$. The results are compatible with both the NEUT 5.4.0 Berger-Sehgal (2009) and GENIE 2.8.0 Rein-Sehgal (2007) model predictions.

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 ^2θ _13 and the impact of priors on the δ _CP measurement. Both analyses prefer the normal mass ordering and upper octant of sin ^2θ _23 with a nearly maximally CP-violating phase. Assuming the normal ordering and using the constraint on sin ^2θ _13 from reactors, sin ^2θ _23=0.561^+0.021_-0.032 using Feldman–Cousins corrected intervals, and m^2_32=2.494_-0.058^+0.041× 10^-3 eV^2 using constant 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 2σ credible level using a flat prior in δ _CP, and just below 2σ using a flat prior in sinδ _CP. When the external constraint on sin ^2θ _13 is removed, sin ^2θ _13=28.0^+2.8_-6.5× 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)×1020 protons on target (POT) in (anti-)neutrino mode at the far detector (FD). Compared to the previous analysis, an additional 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 sin2θ13 and the impact of priors on the δCP measurement. Both analyses prefer the normal mass ordering and upper octant of sin2θ23 with a nearly maximally CP-violating phase. Assuming the normal ordering and using the constraint on sin2θ13 from reactors, sin2θ23=0.561-0.032+0.021 using Feldman-Cousins corrected intervals, and Δm322=2.494-0.058+0.041×10-3eV2 using constant Δχ2 intervals. The CP-violating phase is constrained to δCP=-1.97-0.70+0.97 using Feldman-Cousins corrected intervals, and δCP=0,π is excluded at more than 90% confidence level. A Jarlskog invariant of zero is excluded at more than 2σ credible level using a flat prior in δCP, and just below 2σ using a flat prior in sinδCP. When the external constraint on sin2θ13 is removed, sin2θ13=28.0-6.5+2.8×10-3, in agreement with measurements from reactor experiments. These results are consistent with previous T2K analyses.

We report an updated measurement of the nu(mu)-induced, and the first measurement of the (nu) over bar (mu)- induced coherent charged pion production cross section on C-12 nuclei in the Tokai-to-Kamioka experiment. This is measured in a restricted region of the final- state phase space for which p(mu,pi) > 0.2 GeV, cos(theta(mu)) > 0.8 and cos(theta(pi)) > 0.6, and at a mean ( anti)neutrino energy of 0.85 GeVusing the T2K near detector. The measured nu(mu) charged current coherent pion production flux-averaged cross section on C-12 is (2.98 +/- 0.37(stat) +/- 0.31(syst)(-0.00)(+0.49)(Q(2) model)) x 10(-40) cm(2). The new measurement of the (nu) over bar (mu)-induced cross section on C-12 is (3.05 +/- 0.71(stat) +/- 0.39(syst)(-0.00)(+-0.74) (Q(2) model)) x 10(-40) cm(2). The results are compatible with both the NEUT 5.4.0 Berger-Sehgal (2009) and GENIE 2.8.0 Rein-Sehgal (2007) model predictions.

Muon neutrino and antineutrino disappearance probabilities are identical in the standard three-flavor neutrino oscillation framework, but CPT violation and nonstandard interactions can violate this symmetry. In this work we report the measurements of sin2 theta 23 and Delta m232 independently for neutrinos and antineutrinos. The aforementioned symmetry violation would manifest as an inconsistency in the neutrino and antineutrino oscillation parameters. The analysis discussed here uses a total of 1.97 x 1021 and 1.63 x 1021 protons on target taken with a neutrino and antineutrino beam respectively, and benefits from improved flux and cross section models, new near-detector samples and more than double the data reducing the overall uncertainty of the result. No significant deviation is observed, consistent with the standard neutrino oscillation picture.

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.

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.

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 work is dedicated to the discussion of the possibility of creating a position-sensitive detector with high coordinate reconstruction. The paper presents the simulation results and the experimentally obtained data for a prototype detector based on the MA-20 multianode PMT [1] and a linear stack of scintillating crystal or plastic strips. The multianode position-sensitive PMT MA-20 has a semitransparent bi-alkaline photocathode with the size of the sensitive area of 10 × 200 mm2, 10 evaporated type bi-alkaline type dynodes of the same length, and 20 separated anodes. This PM is the invention of the authors. The maximum gain of the dynode system is 106. The stack of scintillating strips made of GSO (gadolinium orthosilicate) crystals with an element size of 3 × 10 × 50 mm3, of BGO (bismuth germanate) crystals with an element size of 5 × 15 × 40 mm3, and finally stack of strips made of a plastic scintillator with an element size of 5 × 10 × 200 mm3 were used for experimental measurement of a spatial resolution of the detector prototype. Space resolution was determined by the position of the center of gravity of charges of neighboring anodes [2]. As a source of radiation, the collimated 137Cs (γ 0.662 MeV) and 90Sr (β− 2.283 MeV) were used, the measured number of photoelectrons is 10–20 of one element of the stack, depending on the scintillating strip type. The use of a multi-anode photomultiplier in combination with the stack of crystal or plastic scintillators allows one to get a simple linear detector with high performance in spatial resolution and also with a low level of intrinsic noise in comparison, for example, with silicon PMT. A resolution simulation was performed for a system consisting of a one-dimensional stack of scintillation strips placed on the photocathode of a multi-anode PMT for different values of the strips width and the number of photoelectrons of one strip. The experimental dependences of the signal value versus position of optical fiber with a diameter of 1 mm on the photocathode of the 20 anodes PMT were also measured that allowed to specify the coordinate resolution for the described detector. As a result of processing the collected data, spatial resolution was obtained at the level of 1 mm. The obtained results are in good agreement with the simulation results.

Hyper-Kamiokande (HK) is the next generation underground water Cherenkov detector that builds on the highly successful Super-Kamiokande (SK) experiment. The 260,000-ton detector has an 8.4 times larger fiducial volume than its predecessor. HK's low energy threshold combined with the very large fiducial volume make the detector unique; HK is expected to acquire an unprecedented exposure of 3.8 Mton-year over a period of 20 years starting in 2027. It has an extremely diverse science program including long-baseline neutrino oscillation measurements, nucleon decay searches, atmospheric neutrinos, neutrinos from the sun and supernova explosions, and neutrinos from other astrophysical origins. Like DUNE, the flagship project of the U.S. high-energy physics program, HK measures fundamental properties of neutrinos such as the search for leptonic CP violation and neutrino physics beyond the Standard Model.

The DIRAC experiment at CERN investigated in the reaction p(24 GeV/c) + Ni the particle pairs K+K-, pi(+pi)-, and p p over line with relative momentum Q in the pair system less than 100 MeV/c. Because of background influence studies, DIRAC explored three subsamples of K+K- pairs, obtained by subtracting -using the time-of-flight (TOF) technique-the background from initial Q distributions with K+K- sample fractions more than 70%, 50%, and 30%. The corresponding pair distributions in Q and in its longitudinal projection Q(L) were analyzed first in a Coulomb model, which takes into account only the Coulomb final -state interaction (FSI) and assuming pointlike pair production. This Coulomb model analysis leads to a K+K- yield increase of about four at Q(L) = 0.5 MeV/c compared to 100 MeV/c. In order to study contributions from strong interaction, a second more sophisticated model was applied, considering also strong FSI via the resonances f(0)(980) and a(0)(980) and a variable distance r* between the produced K mesons besides Coulomb FSI. This analysis was based on three different parameter sets for the pair production. For the 70% subsample and with the best parameters, 3680 +/- 370 K+K- pairs were found to be compared to 3900 +/- 410 K+K- extracted by means of the Coulomb model. Knowing the efficiency of the TOF cut for background suppression, the total number of detected K+K- pairs was evaluated to be around 40000 +/- 10%, which agrees with the result from the 30% subsample. The K+K- pair number in the 50% subsample differs from the two other values by about three standard deviations, confirming-as discussed in the paper-that experimental data in this subsample is less reliable. In summary, the upgraded DIRAC experiment observed increased K+K- production at small relative momentum Q. The pair distribution in Q is well described by Coulomb FSI, whereas a potential influence from strong interaction in this Q region is insignificant within experimental errors.

We report measurements of the flux-integrated (nu) over bar (mu) and (nu) over bar (mu) + nu(mu) 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(+/-) 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 MeV/c and theta(mu) < 30 degrees, in the laboratory frame. An absence of pions and protons in the detectable phase spaces of p(pi) > 200 MeV/c, theta(pi) < 70 degrees and p(p) > 600 MeV/c, theta(p) < 70 degrees is required. In this paper, both the <(nu)over bar>(mu), cross-sections and (nu) over bar (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 (nu) over bar (mu), cross-section measurements over this phase space are sigma(H2O) = (1.082 +/- 0.068(stat.)(+0.145)(-0.128)(syst.)) x 10(-39) cm(2)/nucleon, sigma(CH) = (1.096 +/- 0.054 (stat.)(+0.132)(-0.117)(syst.)) x 10(-39) cm(2) /nucleon, and sigma(H2O)/sigma(CH) = 0.987 +/- 0.078 (stat.)(+0.093)(-0.090)(syst.). The (nu) over bar (mu), + nu(mu), cross-section is sigma(H2O) = (1.155 +/- 0.064(stat.)(+0.148)(-0.129)(syst.)) x 10(-39) cm(2)/nucleon, sigma(CH) = (1.159 +/- 0.049(stat.)(+0.129)(-0.115)(syst.)) x 10(-39) cm(2)/nucleon, and sigma(H2O)/sigma(CH) = 0.996 +/- 0.069(stat.)(+0.083)(-0.078)(syst.).

This paper reports the first T2K measurement of the transverse kinematic imbalance in the single-$\pi^+$ production channel of neutrino interactions. We measure the differential cross sections in the muon-neutrino charged-current interaction on hydrocarbon with a single $\pi^+$ 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 which have a more realistic treatment of nuclear medium effects including the initial nuclear state and final-state interactions.

We report measurements of the flux-integrated ν̅_μ and ν̅_μ+ν_μ charged-current cross-sections on water and hydrocarbon targets using the T2K anti-neutrino beam, with a mean neutrino 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 nor 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_μ>400 MeV/c and θ_μ<30^∘, in the laboratory frame. Absence of pions and protons in the detectable phase space of "p_π>200 MeV/c and θ_π<70^∘", and "p_ p>600 MeV/c and θ_ p<70^∘" is required. In this paper, both of the ν̅_μ cross-sections and ν̅_μ+ν_μ cross-sections on water and hydrocarbon targets, and their ratios are provided by using D'Agostini unfolding method. The results of the integrated ν̅_μ cross-section measurements over this phase space are σ_ H_2O = (1.082±0.068( stat.)^+0.145_-0.128( syst.)) × 10^-39 cm^2/nucleon, σ_ CH = (1.096±0.054( stat.)^+0.132_-0.117( syst.)) × 10^-39 cm^2/nucleon, and σ_ H_2O/σ_ CH = 0.987±0.078( stat.)^+0.093_-0.090( syst.). The ν̅_μ+ν_μ cross-section is σ_ H_2O = (1.155±0.064( stat.)^+0.148_-0.129( syst.)) × 10^-39 cm^2/nucleon, σ_ CH = (1.159±0.049( stat.)^+0.129_-0.115( syst.)) × 10^-39 cm^2/nucleon, and σ_ H_2O/σ_ CH = 0.996±0.069( stat.)^+0.083_-0.078( syst.).

We report measurements of the flux-integrated $\overline{\nu}_\mu$ and $\overline{\nu}_\mu+\nu_\mu$ 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 $\sigma_{\rm H_{2}O}/\sigma_{\rm CH}=0.996\pm0.069(\rm stat.)^{+0.083}_{-0.078}(\rm syst.)$.

K. Abe, N. Akhlaq, R. Akutsu, A. Ali, C. Alt, C. Andreopoulos, 33 M. Antonova, S. Aoki, T. Arihara, Y. Asada, Y. Ashida, E.T. Atkin, Y. Awataguchi, G.J. Barker, G. Barr, D. Barrow, M. Batkiewicz-Kwasniak, A. Beloshapkin, F. Bench, V. Berardi, L. Berns, S. Bhadra, A. Blanchet, A. Blondel, 12 S. Bolognesi, T. Bonus, B. Bourguille, S.B. Boyd, A. Bravar, D. Bravo Berguño, C. Bronner, S. Bron, A. Bubak, M. Buizza Avanzini, S. Cao, S.L. Cartwright, M.G. Catanesi, A. Cervera, D. Cherdack, G. Christodoulou, M. Cicerchia, ∗ J. Coleman, G. Collazuol, L. Cook, 27 D. Coplowe, A. Cudd, G. De Rosa, T. Dealtry, C.C. Delogu, S.R. Dennis, C. Densham, A. Dergacheva, F. Di Lodovico, S. Dolan, D. Douqa, T.A. Doyle, J. Dumarchez, P. Dunne, A. Eguchi, L. Eklund, S. Emery-Schrenk, A. Ereditato, A.J. Finch, G. Fiorillo, C. Francois, M. Friend, † Y. Fujii, † R. Fukuda, Y. Fukuda, K. Fusshoeller, C. Giganti, M. Gonin, A. Gorin, M. Grassi, M. Guigue, D.R. Hadley, P. Hamacher-Baumann, D.A. Harris, M. Hartz, 27 T. Hasegawa, † S. Hassani, N.C. Hastings, Y. Hayato, 27 A. Hiramoto, M. Hogan, J. Holeczek, N.T. Hong Van, 26 T. Honjo, F. Iacob, A.K. Ichikawa, M. Ikeda, T. Ishida, † M. Ishitsuka, K. Iwamoto, A. Izmaylov, N. Izumi, M. Jakkapu, B. Jamieson, S.J. Jenkins, C. Jesús-Valls, P. Jonsson, C.K. Jung, ‡ P.B. Jurj, M. Kabirnezhad, H. Kakuno, J. Kameda, S.P. Kasetti, Y. Kataoka, Y. Katayama, T. Katori, E. Kearns, 27, ‡ M. Khabibullin, A. Khotjantsev, T. Kikawa, H. Kikutani, S. King, J. Kisiel, T. Kobata, T. Kobayashi, † L. Koch, A. Konaka, L.L. Kormos, Y. Koshio, ‡ A. Kostin, K. Kowalik, Y. Kudenko, § S. Kuribayashi, R. Kurjata, T. Kutter, M. Kuze, L. Labarga, J. Lagoda, M. Lamoureux, D. Last, M. Laveder, M. Lawe, R.P. Litchfield, S.L. Liu, A. Longhin, L. Ludovici, X. Lu, T. Lux, L.N. Machado, L. Magaletti, K. Mahn, M. Malek, S. Manly, L. Maret, A.D. Marino, L. Marti-Magro, 27 T. Maruyama, † T. Matsubara, K. Matsushita, C. Mauger, K. Mavrokoridis, E. Mazzucato, N. McCauley, J. McElwee, K.S. McFarland, C. McGrew, A. Mefodiev, M. Mezzetto, A. Minamino, O. Mineev, S. Mine, M. Miura, ‡ L. Molina Bueno, S. Moriyama, ‡ Th.A. Mueller, L. Munteanu, Y. Nagai, T. Nakadaira, † M. Nakahata, 27 Y. Nakajima, A. Nakamura, K. Nakamura, 15, † Y. Nakano, S. Nakayama, 27 T. Nakaya, 27 K. Nakayoshi, † C.E.R. Naseby, T.V. Ngoc, ¶ V.Q. Nguyen, K. Niewczas, Y. Nishimura, E. Noah, T.S. Nonnenmacher, F. Nova, J. Nowak, J.C. Nugent, H.M. O’Keeffe, L. O’Sullivan, T. Odagawa, T. Ogawa, R. Okada, K. Okumura, 27 T. Okusawa, R.A. Owen, Y. Oyama, † V. Palladino, V. Paolone, M. Pari, W.C. Parker, S. Parsa, J. Pasternak, M. Pavin, D. Payne, G.C. Penn, L. Pickering, C. Pidcott, G. Pintaudi, C. Pistillo, B. Popov, ∗∗ K. Porwit, M. Posiadala-Zezula, A. Pritchard, B. Quilain, T. Radermacher, E. Radicioni, B. Radics, P.N. Ratoff, C. Riccio, E. Rondio, S. Roth, A. Rubbia, A.C. Ruggeri, C. Ruggles, A. Rychter, K. Sakashita, † F. Sánchez, G. Santucci, C.M. Schloesser, K. Scholberg, ‡ M. Scott, Y. Seiya, †† T. Sekiguchi, † H. Sekiya, 27, ‡ D. Sgalaberna, A. Shaikhiev, A. Shaykina, M. Shiozawa, 27 W. Shorrock, A. Shvartsman, K. Skwarczynski, M. Smy, J.T. Sobczyk, H. Sobel, 27 F.J.P. Soler, Y. Sonoda, R. Spina, S. Suvorov, 50 A. Suzuki, S.Y. Suzuki, † Y. Suzuki, A.A. Sztuc, M. Tada, † M. Tajima, A. Takeda, Y. Takeuchi, 27 H.K. Tanaka, ‡ Y. Tanihara, M. Tani, N. Teshima, L.F. Thompson, W. Toki, C. Touramanis, T. Towstego, K.M. Tsui, T. Tsukamoto, † M. Tzanov, Y. Uchida, M. Vagins, 4 S. Valder, D. Vargas, G. Vasseur, C. Vilela, W.G.S. Vinning, T. Vladisavljevic, T. Wachala, J. Walker, J.G. Walsh, Y. Wang, D. Wark, 41 M.O. Wascko, A. Weber, 41 R. Wendell, ‡ M.J. Wilking, C. Wilkinson, J.R. Wilson, K. Wood, C. Wret, J. Xia, K. Yamamoto, †† C. Yanagisawa, ‡‡ G. Yang, T. Yano, K. Yasutome, N. Yershov, M. Yokoyama, ‡ T. Yoshida, Y. Yoshimoto, M. Yu, A. Zalewska, J. Zalipska, K. Zaremba, G. Zarnecki, M. Ziembicki, M. Zito, and S. Zsoldos

Supernovae are among the most magnificent events in the observable universe. They produce many of the chemical elements necessary for life to exist and their remnants---neutron stars and black holes---are interesting astrophysical objects in their own right. However, despite millennia of observations and almost a century of astrophysical study, the explosion mechanism of supernovae is not yet well understood. Hyper-Kamiokande is a next-generation neutrino detector that will be able to observe the neutrino flux from the next galactic supernova in unprecedented detail. In this thesis, I investigate how well such an observation would allow us to reconstruct the explosion mechanism. I develop a high-precision supernova event generator and use a detailed detector simulation and event reconstruction to explore Hyper-Kamiokande's response to five supernova models simulated by different groups around the world. I show that 300 neutrino events in Hyper-Kamiokande---corresponding to a supernova at a distance of at least 60 kpc---are sufficient to distinguish between these models with high accuracy. These findings indicate that, once the next galactic supernova happens, Hyper-Kamiokande will be able to determine details of the supernova explosion mechanism.

We report measurements by the T2K experiment of the parameters $\theta_23$ and $\Delta m^2_{32}$ which govern the disappearance of muon neutrinos and antineutrinos in the three-flavor PMNSneutrino 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 $1.49\times 10^{21}$ protons on target (POT) in neutrino mode and $1.64\times 10^21$ POT in antineutrino mode are used. Assuming the normal neutrino mass ordering the best-fit values obtained by T2K were $\sin^2\theta_{23}=0.51^{+0.06}_{-0.07}$ $(0.43^{+0.21}_{-0.05})$ and $\Delta m^2_{32}=2.47^{+0.08}_{-0.09} (2.50^{+0.18}_{-0.13})$ $eV^2/c^4$. 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-flavour neutrino oscillation model where the sine of the mixing angle is allowed to take non-physical 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.