Upper bound on neutrino mass based on T2K neutrino timing measurements

The Tokai to Kamioka (T2K) long-baseline neutrino experiment consists of a muon neutrino beam, produced at the J-PARC accelerator, a near detector complex and a large 295-km-distant far detector. The present work utilizes the T2K event timing measurements at the near and far detectors to study neutrino time of flight as a function of derived neutrino energy. Under the assumption of a relativistic relation between energy and time of flight, constraints on the neutrino rest mass can be derived. The sub-GeV neutrino beam in conjunction with timing precision of order tens of ns provide sensitivity to neutrino mass in the few MeV/c2 range. We study the distribution of relative arrival times of muon and electron neutrino candidate events at the T2K far detector as a function of neutrino energy. The 90% C.L. upper limit on the mixture of neutrino mass eigenstates represented in the data sample is found to be mν2\u3c5.6 MeV2/c4

Updated T2K measurements of muon neutrino and antineutrino disappearance using 1.5×1021 protons on target

We report measurements by the T2K experiment of the parameters θ23 and Δm322 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)=0.51-0.07+0.08 and Δm322=2.53-0.13+0.15×10-3 eV2/c4 for neutrinos, and sin2(θ-23)=0.42-0.07+0.25 and Δm-232=2.55-0.27+0.33×10-3 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

Combined Analysis of Neutrino and Antineutrino Oscillations at T2K

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

Search for short baseline νe disappearance with the T2K near detector

The T2K experiment has performed a search for νe disappearance due to sterile neutrinos using 5.9×1020 protons on target for a baseline of 280 m in a neutrino beam peaked at about 500 MeV. A sample of νe CC interactions in the off-axis near detector has been selected with a purity of 63% and an efficiency of 26%. The p-value for the null hypothesis is 0.085 and the excluded region at 95% C.L. is approximately sin22θee\u3e0.3 for Δmeff2\u3e7eV2/c4

Measurement of the νμcharged current quasielastic cross section on carbon with the T2K on-axis neutrino beam

We report a measurement of the νμcharged current quasielastic cross-sections on carbon in the T2K on-axis neutrino beam. The measured charged current quasielastic cross-sections on carbon at mean neutrino energies of 1.94 GeVand 0.93 GeVare (11.95 ± 0.19(stat)-1.47+1.82(syst)) × 10-39cm2/neutron, and (10.64 ± 0.37(stat)-1.65+2.03(syst)) × 10-39cm2/neutron, respectively. These results agree well with the predictions of neutrino interaction models. In addition, we investigated the effects of the nuclear model and the multi-nucleon interaction

Measurement of the electron neutrino charged-current interaction rate on water with the T2K ND280 π0 detector

This paper presents a measurement of the charged current interaction rate of the electron neutrino beam component of the beam above 1.5 GeV using the large fiducial mass of the T2K π0 detector. The predominant portion of the νe flux (∼85%) at these energies comes from kaon decays. The measured ratio of the observed beam interaction rate to the predicted rate in the detector with water targets filled is 0.89±0.08(stat)±0.11(sys), and with the water targets emptied is 0.90±0.09(stat)±0.13(sys). The ratio obtained for the interactions on water only from an event subtraction method is 0.87±0.33(stat)±0.21(sys). This is the first measurement of the interaction rate of electron neutrinos on water, which is particularly of interest to experiments with water Cherenkov detectors

Measurement of double-differential muon neutrino charged-current interactions on C8 H8 without pions in the final state using the T2K off-axis beam

We report the measurement of muon neutrino charged-current interactions on carbon without pions in the final state at the T2K beam energy using 5.734×1020 protons on target. For the first time the measurement is reported as a flux-integrated, double-differential cross section in muon kinematic variables (cosθμ, pμ), without correcting for events where a pion is produced and then absorbed by final state interactions. Two analyses are performed with different selections, background evaluations and cross-section extraction methods to demonstrate the robustness of the results against biases due to model-dependent assumptions. The measurements compare favorably with recent models which include nucleon-nucleon correlations but, given the present precision, the measurement does not distinguish among the available models. The data also agree with Monte Carlo simulations which use effective parameters that are tuned to external data to describe the nuclear effects. The total cross section in the full phase space is σ=(0.417±0.047(syst)±0.005(stat))×10-38 cm2 nucleon-1 and the cross section integrated in the region of phase space with largest efficiency and best signal-over-background ratio (cosθμ\u3e0.6 and pμ\u3e200 MeV) is σ=(0.202±0.036(syst)±0.003(stat))×10-38 cm2 nucleon-1

Measurement of the νμ charged-current quasielastic cross section on carbon with the ND280 detector at T2K

This paper reports a measurement by the T2K experiment of the νμ charged current quasielastic (CCQE) cross section on a carbon target with the off-axis detector based on the observed distribution of muon momentum (pμ) and angle with respect to the incident neutrino beam (θμ). The flux-integrated CCQE cross section was measured to be «

First measurement of the muon neutrino charged current single pion production cross section on water with the T2K near detector

The T2K off-axis near detector, ND280, is used to make the first differential cross section measurements of muon neutrino charged current single positive pion production on a water target at energies ∼0.8 GeV. The differential measurements are presented as a function of the muon and pion kinematics, in the restricted phase space defined by pπ+\u3e200 MeV/c, pμ\u3e200 MeV/c, cos(θπ+)\u3e0.3 and cos(θμ)\u3e0.3. The total flux integrated νμ charged current single positive pion production cross section on water in the restricted phase space is measured to be

Measurement of Coherent π+ Production in Low Energy Neutrino-Carbon Scattering

We report the first measurement of the flux-averaged cross section for charged current coherent π+ production on carbon for neutrino energies less than 1.5 GeV, and with a restriction on the final state phase space volume in the T2K near detector, ND280. Comparisons are made with predictions from the Rein-Sehgal coherent production model and the model by Alvarez-Ruso et al., the latter representing the first implementation of an instance of the new class of microscopic coherent models in a neutrino interaction Monte Carlo event generator. We observe a clear event excess above background, disagreeing with the null results reported by K2K and SciBooNE in a similar neutrino energy region. The measured flux-averaged cross sections are below those predicted by both the Rein-Sehgal and Alvarez-Ruso et al. models