T violation at a future neutrino factory (Contribution to the 25th International Workshop on Neutrinos from Accelerators)

TL;DR

This paper explores the potential to measure T violation in future neutrino experiments using a neutrino factory and Hyper-Kamiokande, enabling insights into the CP phase and testing the three neutrino paradigm.

Contribution

It proposes a method to measure T violation and the CP phase in future neutrino experiments with minimal matter density uncertainties, providing a new test of neutrino physics.

Findings

T violation can be measured with good accuracy at Hyper-Kamiokande.

The CP phase δ can be determined if |sin(δ)| is large enough.

The method is insensitive to Earth's matter density uncertainties.

Abstract

We study the possibility of measuring T (time reversal) violation in a future long baseline neutrino oscillation experiment. By assuming a neutrino factory as a staging scenario of a muon collider at the J-PARC site, we find that the $\nu_e \to \nu_\mu$ oscillation probabilities can be measured with good accuracy at the Hyper-Kamiokande detector. By comparing with the probability of the time-reversal process, $\nu_\mu \to \nu_e$, measured at the T2K/T2HK, one can determine the CP phase $\delta$ in the neutrino mixing matrix if $|\sin(\delta)|$ is large enough. The determination of $\delta$ can be made with poor knowledge of the matter density of the earth as T violation is almost insensitive to the matter effects. The comparison of CP and T-violation measurements, {\it \`a la} the CPT theorem, provides us with a non-trivial check of the three neutrino paradigm based on the quantum field theory. This proceeding is based on JHEP 12 (2024), 014 [arXiv:hep-ph/2407.05807].