Abstract: This paper reports on the search for heavy neutrinos with masses in the range 140 < M-N < 493 MeV/c(2) 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(alpha)(+/-)pi(-/+) and N -> l(alpha)(+)l(beta)nu (-(-))= (alpha, beta = e, mu). 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 (U-e(2), U-mu(2), U-tau(2)) as a function of the heavy neutrino mass, e.g., U-e(2) < 10(-9) at 90% C.L. for a mass of 390 MeV/c(2). These constraints are competitive with previous experiments.

Abstract: The T2K experiment presents new measurements of neutrino oscillation parameters using 19.7(16.3) x 10(20) protons on target (POT) in (anti-)neutrino mode at the far detector (FD). Compared to the previous analysis, an additional 4.7 x 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) and the impact of priors on the delta(CP) measurement. Both analyses prefer the normal mass ordering and upper octant of sin(2) theta(23) with a nearly maximally CP-violating phase. Assuming the normal ordering and using the constraint on sin(2) theta(13) from reactors, sin(2) theta(23) = 0.561(-0.032)(+0.021) using Feldman-Cousins corrected intervals, and Delta m(32)(2) = 2.494(-0.058)(+0.041) x 10(-3) eV(2) using constant Delta chi(2) intervals. The CP-violating phase is constrained to delta(CP) = -1.97(-0.70)(+0.97) using Feldman-Cousins corrected intervals, and delta(CP) = 0, pi is excluded at more than 90% confidence level. A Jarlskog invariant of zero is excluded at more than 2 sigma credible level using a flat prior in delta(CP), and just below 2 sigma using a flat prior in sin delta(CP). When the external constraint on sin(2) nu(13) is removed, sin(2) theta(13) = 28.0(-6.5)(+2.8) x 10(-3), in agreement with measurements from reactor experiments. These results are consistent with previous T2K analyses.

Abstract: 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.

Abstract: Liquid argon time projection chamber detector technology provides high spatial and calorimetric resolutions on the charged particles traversing liquid argon. As a result, the technology has been used in a number of recent neutrino experiments, and is the technology of choice for the Deep Underground Neutrino Experiment (DUNE). In order to perform high precision measurements of neutrinos in the detector, final state particles need to be effectively identified, and their energy accurately reconstructed. This article proposes an algorithm based on a convolutional neural network to perform the classification of energy deposits and reconstructed particles as track-like or arising from electromagnetic cascades. Results from testing the algorithm on experimental data from ProtoDUNE-SP, a prototype of the DUNE far detector, are presented. The network identifies track- and shower-like particles, as well as Michel electrons, with high efficiency. The performance of the algorithm is consistent between experimental data and simulation.

Abstract: The rapid development of general-purpose computing on graphics processing units (GPGPU) is allowing the implementation of highly-parallelized Monte Carlo simulation chains for particle physics experiments. This technique is particularly suitable for the simulation of a pixelated charge readout for time projection chambers, given the large number of channels that this technology employs. Here we present the first implementation of a full microphysical simulator of a liquid argon time projection chamber (LArTPC) equipped with light readout and pixelated charge readout, developed for the DUNE Near Detector. The software is implemented with an end-to-end set of GPU-optimized algorithms. The algorithms have been written in Python and translated into CUDA kernels using Numba, a just-in-time compiler for a subset of Python and NumPy instructions. The GPU implementation achieves a speed up of four orders of magnitude compared with the equivalent CPU version. The simulation of the current induced on 103 pixels takes around 1 ms on the GPU, compared with approximately 10 s on the CPU. The results of the simulation are compared against data from a pixel-readout LArTPC prototype.