T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Izmaylov, A., & Novella, P. (2017). Measurement of neutrino and antineutrino oscillations by the T2K experiment including a new additional sample of nu(e) interactions at the far detector. Phys. Rev. D, 96(9), 092006–49pp.
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).
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Izmaylov, A., & Novella, P. (2018). First measurement of the nu(mu) charged-current cross section on a water target without pions in the final state. Phys. Rev. D, 97(1), 012001–16pp.
Abstract: This paper reports the first differential measurement of the charged-current interaction cross section of nu(mu) on water with no pions in the final state. This flux-averaged measurement has been made using the T2K experiment's off-axis near detector, and is reported in doubly differential bins of muon momentum and angle. The flux-averaged total cross section in a restricted region of phase space was found to be sigma = (0.95 +/- 0.08(stat) +/- 0.06(det syst) +/- 0.04(model syst) +/- 0.08(flux)) x 10(-38) cm(2)/n.
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., & Novella, P. (2020). Simultaneous measurement of the muon neutrino charged-current cross section on oxygen and carbon without pions in the final state at T2K. Phys. Rev. D, 101(11), 112004–32pp.
Abstract: This paper reports the first simultaneous measurement of the double differential muon neutrino chargedcurrent 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.
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., & Novella, P. (2021). Measurements of (nu)over-bar(mu) and (nu)over-bar(mu) + nu(mu) charged-current cross-sections without detected pions or protons on water and hydrocarbon at a mean anti-neutrino energy of 0.86 GeV. Prog. Theor. Exp. Phys., 2021(4), 043C01–28pp.
Abstract: 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.).
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., Molina Bueno, L., & Novella, P. (2022). Scintillator ageing of the T2K near detectors fro 2010 to 2021. J. Instrum., 17(10), P10028–36pp.
Abstract: 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 long component of the attenuation length of the wavelength shifting fibres was observed to degrade by 1.3-5.4% per year, while the short component of the attenuation length did not show any conclusive degradation.
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., Molina Bueno, L., & Novella, P. (2023). Measurements of neutrino oscillation parameters from the T2K experiment using 3.6 x 10^21 protons on target. Eur. Phys. J. C, 83(9), 782–50pp.
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.
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., Molina Bueno, L., & Novella, P. (2023). Updated T2K measurements of muon neutrino and antineutrino disappearance using 3.6 x 10^21 protons on target. Phys. Rev. D, 108(7), 072011–10pp.
Abstract: 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.
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., Molina Bueno, L., & Novella, P. (2023). Measurements of the νμ and bar(ν)μ-induced coherent charged pion production cross sections on 12C by the T2K experiment. Phys. Rev. D, 108(9), 092009–15pp.
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.
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., Molina Bueno, L., & Novella, P. (2023). First measurement of muon neutrino charged-current interactions on hydrocarbon without pions in the final state using multiple detectors with correlated energy spectra at T2K. Phys. Rev. D, 108(11), 112009–32pp.
Abstract: 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.
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., & Molina Bueno, L. (2021). Improved constraints on neutrino mixing from the T2K experiment with 3.13 x 10(21) protons on target. Phys. Rev. D, 103(11), 112008–59pp.
Abstract: The T2K experiment reports updated measurements of neutrino and antineutrino oscillations using both appearance and disappearance channels. This result comes from an exposure of 14.9(16.4) x 10(20) protons on target in neutrino (antineutrino) mode. Significant improvements have been made to the neutrino interaction model and far detector reconstruction. An extensive set of simulated data studies have also been performed to quantify the effect interaction model uncertainties have on the T2K oscillation parameter sensitivity. T2K performs multiple oscillation analyses that present both frequentist and Bayesian intervals for the Pontecorvo-Maki-Nakagawa-Sakata parameters. For fits including a constraint on sin(2)theta(13) from reactor data and assuming normal mass ordering T2K measures sin(2)theta(13) = 0.53(-0.04)(+0.03) and Delta m(32)(2) = (2.45 +/- 0.07) x 10(-3) eV(2) c(-4). The Bayesian analyses show a weak preference for normal mass ordering 89)% posterior probability) and the upper sin(2)theta(13) octant (80% posterior probability), with a uniform prior probability assumed in both cases. The T2K data exclude CP conservation in neutrino oscillations at the 2 sigma level.
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