First combined analysis of neutrino and antineutrino oscillations at T2K

TL;DR

This paper presents the first combined analysis of neutrino and antineutrino oscillations at T2K, providing evidence against CP conservation and constraining the CP-violating phase using extensive experimental data.

Contribution

It is the first to jointly analyze neutrino and antineutrino oscillation data at T2K, improving constraints on CP violation in the lepton sector.

Findings

CP conservation hypothesis is excluded at 90% confidence level.

The 90% confidence interval for δ_CP is (-3.13, -0.39).

Data favor CP violation in neutrino oscillations.

Abstract

T2K reports its first results in the search for CP violation in neutrino oscillations using appearance and disappearance channels for neutrino- and antineutrino-mode beam. The data include all runs from Jan 2010 to May 2016 and comprise $7.482\times10^{20}$,protons on target in neutrino mode, which yielded in the far detector 32 e-like and 135 $\mu$-like events, and $7.471\times10^{20}$,protons on target in antineutrino mode which yielded 4 e-like and 66 $\mu$-like events. Reactor measurements of $\sin^{2}2\theta_{13}$ have been used as an additional constraint. The one-dimensional confidence interval at 90% for $\delta_{CP}$ spans the range ($-3.13$, $-0.39$) for normal mass ordering. The CP conservation hypothesis ($\delta_{CP}=0,\pi$) is excluded at 90% C.L.