Search for CP violation in Neutrino and Antineutrino Oscillations by the T2K experiment with $2.2\times10^{21}$ protons on target

TL;DR

The T2K experiment investigates CP violation in neutrino oscillations, providing evidence that disfavors CP-conserving values of the CP-violating phase with current experimental data.

Contribution

This study presents the first constraints on the CP-violating phase using T2K data with a large proton exposure, indicating potential CP violation in neutrino oscillations.

Findings

Observed 89 electron neutrino candidates versus 67.5 expected for no CP violation.

The 2σ confidence interval for δ_CP excludes CP-conserving values.

Measured mixing parameters are consistent with previous results.

Abstract

The T2K experiment measures muon neutrino disappearance and electron neutrino appearance in accelerator-produced neutrino and antineutrino beams. With an exposure of $14.7(7.6)\times 10^{20}$ protons on target in neutrino (antineutrino) mode, 89 $\nu_e$ candidates and 7 anti-$\nu_e$ candidates were observed while 67.5 and 9.0 are expected for $\delta_{CP}=0$ and normal mass ordering. The obtained $2\sigma$ confidence interval for the $CP$ violating phase, $\delta_{CP}$, does not include the $CP$-conserving cases ($\delta_{CP}=0,\pi$). The best-fit values of other parameters are $\sin^2\theta_{23} = 0.526^{+0.032}_{-0.036}$ and $\Delta m^2_{32}=2.463^{+0.071}_{-0.070}\times10^{-3} \mathrm{eV}^2/c^4$.