First joint oscillation analysis of Super-Kamiokande atmospheric and T2K accelerator neutrino data
The Super-Kamiokande and T2K collaborations present a joint measurement of neutrino oscillation parameters from their atmospheric and beam neutrino data. A common neutrino interaction model has been developed for the events of the two experiments which overlap in energy, and correlations between their detector systematic uncertainties were evaluated. Using 3244.4 days of atmospheric data and a beam exposure of respectively 19.7E20 and 16.3E20 protons on target in neutrino and antineutrino running modes, we find an exclusion of the CP-conserving value of the Jarlskog invariant with a significance varying between 1.9σ and 2.0σ depending on the analysis considered, a limited preference for the normal mass ordering (MO), and no strong preference for the θ23 octant.
arXiv preprint : https://arxiv.org/pdf/2405.12488
Updated T2K measurements of muon neutrino and antineutrino disappearance using 3.6E21 protons on target
https://arxiv.org/abs/2305.09916Muon neutrino and antineutrino disappearance probabilities are identical in the standard three-flavor neutrino oscillation framework, but CPT violation and non-standard interactions can violate this symmetry. In this work we report the measurements of sin2θ23 and Δm232 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 1.97E21 and 1.63E21 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.
arXiv preprint : https://arxiv.org/pdf/2305.09916
Data release : https://zenodo.org/record/7929975
Measurements of neutrino oscillation parameters from the T2K experiment using 3.6E21 protons on target
Scintillator ageing of the T2K near detectors from 2010 to 2021
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.
arXiv preprint: https://arxiv.org/abs/2207.12982
Data release: https://doi.org/10.5281/zenodo.6783269
DOI: https://doi.org/10.1088/1748-0221/17/10/P10028
Reference: JINST 17 (2022) 10, P10028
Search for Electron Antineutrino Appearance in a Long-baseline Muon Antineutrino Beam
Electron antineutrino appearance is measured by the T2K experiment in an accelerator-produced antineutrino beam, using additional neutrino beam operation to constrain parameters of the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix. T2K observes 15 candidate electron antineutrino events with a background expectation of 9.3 events. Including information from the kinematic distribution of observed events, the hypothesis of no electron antineutrino appearance is disfavored with a significance of 2.40σ and no discrepancy between data and PMNS predictions is found. A complementary analysis that introduces an additional free parameter which allows non-PMNS values of electron neutrino and antineutrino appearance also finds no discrepancy between data and PMNS predictions.
arXiv preprint: https://arxiv.org/abs/1911.07283
DOI: https://doi.org/10.1103/PhysRevLett.124.161802
Reference: Phys.Rev.Lett. 124 (2020) 16, 161802
Measurements of νμ-bar and νμ-bar+νμ charged-current cross-sections without detected pions or protons on water and hydrocarbon at a mean anti-neutrino energy of 0.86 GeV
We report measurements of the flux-integrated |νμ-bar| and |νμ-bar+| 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 || 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.
Improved constraints on neutrino mixing from the T2K experiment with 3.13×10E21 protons on target
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)×10E20 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 sin2θ13 from reactor data and assuming normal mass ordering T2K measures sin2θ23=0.53-0.04+0.03 and Δm322=(2.45±0.07)×10-3 eV2 c-4. The Bayesian analyses show a weak preference for normal mass ordering (89% posterior probability) and the upper sin2θ23 octant (80% posterior probability), with a uniform prior probability assumed in both cases. The T2K data exclude CP conservation in neutrino oscillations at the 2σ level.
First T2K measurement of transverse kinematic imbalance in the muon-neutrino charged-current single-π+ production channel containing at least one proton
This paper reports the first T2K measurement of the transverse kinematic imbalance in the single- production channel of neutrino interactions. We measure the differential cross sections in the muon-neutrino charged-current interaction on hydrocarbon with a single- 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.
Simultaneous measurement of the muon neutrino charged-current cross section on oxygen and carbon without pions in the final state at T2K
This paper reports the first simultaneous measurement of the double differential muon neutrinocharged-current cross section on oxygen and carbon without pions in the final state as a function ofthe 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 oscillationanalyses. 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-goingmuons. Overall, of the models tested, the result is best described using Local Fermi Gas descriptionsof the nuclear ground state with RPA suppression.
T2K measurements of muon neutrino and antineutrino disappearance using 3.13E21 protons on target
We report measurements by the T2K experiment of the parameters θ23 and Δm322, which govern the disappearance of muon neutrinos and antineutrinos in the three-flavor PMNS neutrino 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 1.49×1021 protons on target (POT) in neutrino mode and 1.64×1021 POT in antineutrino mode are used. The best-fit values obtained by T2K were sin2(θ23)=0.51-0.07+0.06(0.43-0.05+0.21) and Δm322=2.47-0.09+0.08(2.50-0.13+0.18)×10-3 eV2/c4 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-flavor neutrino oscillation model where the sine of the mixing angle is allowed to take nonphysical 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.
