Abstract: Noble element time projection chambers are a leading technology for rare event detection in physics, such as for dark matter and neutrinoless double beta decay searches. Time projection chambers typically assign event position in the drift direction using the relative timing of prompt scintillation and delayed charge collection signals, allowing for reconstruction of an absolute position in the drift direction. In this paper, alternate methods for assigning event drift distance via quantification of electron diffusion in a pure high pressure xenon gas time projection chamber are explored. Data from the NEXT-White detector demonstrate the ability to achieve good position assignment accuracy for both high- and low-energy events. Using point-like energy deposits from Kr-83m calibration electron captures (E similar to 45 keV), the position of origin of low-energy events is determined to 2 cm precision with bias <1 mm. A convolutional neural network approach is then used to quantify diffusion for longer tracks (E >= 1.5 MeV), from radiogenic electrons, yielding a precision of 3 cm on the event barycenter. The precision achieved with these methods indicates the feasibility energy calibrations of better than 1% FWHM at Q(beta beta) in pure xenon, as well as the potential for event fiducialization in large future detectors using an alternate method that does not rely on primary scintillation.

Abstract: 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 similar to 0.8 GeV. The differential measurements are presented as a function of the muon and pion kinematics, in the restricted phase space defined by p(pi+) > 200 MeV/c, p(mu) > 200 MeV/c, cos(theta(pi+)) > 0.3 and cos(theta(mu)) > 0.3. The total flux integrated nu(mu) charged current single positive pion production cross section on water in the restricted phase space is measured to be <sigma >(phi) = 4.25 +/- 0.48(stat) +/- 1.56(syst) x 10(-40) cm(2)/nucleon. The total cross section is consistent with the NEUT prediction (5.03 x 10(-40) cm(2)/nucleon) and 2 sigma lower than the GENIE prediction (7.68 x 10(-40) cm(2)/nucleon). The differential cross sections are in good agreement with the NEUT generator. The GENIE simulation reproduces well the shapes of the distributions, but overestimates the overall cross section normalization.

Abstract: We report measurements by the T2K experiment of the parameters theta(23) and Delta m(32)(2) 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 x 10(20) POT in neutrino running mode and 7.471 x 10(20) POT in antineutrino mode, T2K obtained sin(2) (theta(23)) = 0.51(-0.07)(+0.08) and Delta (m) over bar (2)(32) = (+0.15)(-2.53) -0.13 x 10(-3) eV(2)/c(4) for neutrinos, and sin(2) ((theta) over bar (23)) = 0.42(-0.07)(+0.25) and Delta(m) over bar (2)(32) = 2.55(-0.27)(+0.33) x 10(-3) eV(2)/c(4) 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.

Abstract: The T2K experiment reports an updated analysis of neutrino and antineutrino oscillations in appearance and disappearance channels. A sample of electron neutrino candidates at Super-Kamiokande in which a pion decay has been tagged is added to the four single-ring samples used in previous T2K oscillation analyses. Through combined analyses of these five samples, simultaneous measurements of four oscillation parameters, vertical bar Delta m(32)(2)vertical bar, sin(2) theta(23), sin(2) theta(13), and delta(CP) and of the mass ordering are made. A set of studies of simulated data indicates that the sensitivity to the oscillation parameters is not limited by neutrino interaction model uncertainty. Multiple oscillation analyses are performed, and frequentist and Bayesian intervals are presented for combinations of the oscillation parameters with and without the inclusion of reactor constraints on sin(2) theta(13). When combined with reactor measurements, the hypothesis of CP conservation (delta(CP) = 0 or pi) is excluded at 90% confidence level. The 90% confidence region for delta(CP) is [-2.95, -0.44] ([-1.47, -1.27]) for normal (inverted) ordering. The central values and 68% confidence intervals for the other oscillation parameters for normal (inverted) ordering are Delta m(32)(2) = 2.54 +/- 0.08(2.51 +/- 0.08) x 10(-3) eV(2)/c(4) and sin(2) theta(23) = 0.55(-0.09)(+0.005) (0.55(-0.08)(+0.05)), compatible with maximal mixing. In the Bayesian analysis, the data weakly prefer normal ordering (Bayes factor 3.7) and the upper octant for sin(2) theta(23) (Bayes factor 2.4).

Abstract: The single pi(0) production rate in neutral current neutrino interactions on water in a neutrino beam with a peak neutrino energy of 0.6 GeV has been measured using the empty set, one of the subdetectors of the T2K near detector. The production rate was measured for data taking periods when the Pempty setD contained water (2.64 x 10(20) protons-on-target) and also periods without water (3.49 x 10(20) protons-on-target). A measurement of the neutral current single pi(0) production rate on water is made using appropriate subtraction of the production rate with water in from the rate with water out of the target region. The subtraction analysis yields 106 +/- 41 +/- 69 signal events where the uncertainties are statistical (stat.) and systematic (sys.) respectively. This is consistent with the prediction of 157 events from the nominal simulation. The measured to expected ratio is 0.68 +/- 0.26(stat) +/- 0.44(sys) +/- 0.12(flux). The nominal simulation uses a flux integrated cross section of 7.63 x 10(-39) cm(2) per nucleon with an average neutrino interaction energy of 1.3 GeV.