T violation at a future neutrino factory

TL;DR

This paper explores the potential to measure T violation in future neutrino experiments using a neutrino factory and Hyper-Kamiokande, providing a new way to test the neutrino mixing paradigm with minimal matter effect interference.

Contribution

It proposes a novel experimental setup combining a neutrino factory and Hyper-Kamiokande to measure T violation and determine the CP phase in neutrino oscillations.

Findings

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

Comparison of T and CP violation allows testing the three neutrino paradigm.

Matter density uncertainties have little impact on T violation measurements.

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 a 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 experiments, 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.