Results from the T2K experiment on neutrino mixing including a new far detector $\mu$-like sample

TL;DR

This paper reports improved measurements of neutrino mixing parameters from the T2K experiment, including new data samples and refined modeling, supporting the normal mass ordering and specific values for mixing angles and CP phase.

Contribution

The study introduces new muon-neutrino samples with tagged pions and enhanced flux and interaction models, advancing the precision of neutrino oscillation measurements.

Findings

Preference for normal mass ordering

Upper octant of $ heta_{23}$ favored

Best-fit CP phase near maximal value

Abstract

We have made improved measurements of three-flavor neutrino mixing with 19.7(16.3)$\times 10^{20}$ protons on target in (anti-)neutrino-enhanced beam modes. A new sample of muon-neutrino events with tagged pions has been added at the far detector, as well as new proton and photon-tagged samples at the near detector. Significant improvements have been made to the flux and neutrino interaction modeling. T2K data continue to prefer the normal mass ordering and upper octant of $\sin^2\theta_{23}$ with a near-maximal value of the charge-parity violating phase with best-fit values in the normal ordering of $\delta_{\scriptscriptstyle\mathrm{CP}}=-2.18\substack{+1.22 \\ -0.47}$, $\sin^2\theta_{23}=0.559\substack{+0.018 \\ -0.078}$ and $\Delta{}m^2_{32}=(+2.506\substack{+0.039 \\ -0.052})\times 10^{-3}$ eV$^{2}$.