March 16, 2023
The T2K experiment presents new constraints on the neutrino oscillation parameters, using 3.6E21 protons on target (POT). The results include world-leading constraints on the CP-violating phase, delta CP, the Jarlskog invariant, and the atmospheric oscillation parameters.
This analysis increases the data at the far detector by 4.7E20 POT neutrino data on the previous result, and sees significant improvements to the analysis methodology. The near-detector analysis includes more than double the data, and uses new selections. Additionally, this is the first T2K oscillation analysis to use NA61/SHINE hadron scattering data on a replica of the T2K target to tune the neutrino flux model, leading to a reduction of flux uncertainties from 9% to 5% in the neutrino flux peak. The neutrino interaction model was also improved to include new nuclear effects and calculations.
The normal ordering and upper octant is favoured, with a nearly maximally CP violating phase, consistent with previous results. The analysis excludes delta CP=0 and pi at more than 90% confidence level. It also excludes a Jarlskog invariant of zero at more than 2 sigma credible level with a flat prior in delta CP, and just below 2 sigma using a flat prior in sin delta CP. Furthermore, the analysis finds a sin^2 theta_{13} consistent with the reactor experiments.
