Should T2K run in dominant neutrino mode to detect CP violation ?

TL;DR

This paper argues that T2K should primarily run in neutrino mode to optimize CP violation detection, leveraging combined data with other experiments to resolve degeneracies and maximize sensitivity.

Contribution

It proposes a strategy for T2K to focus on neutrino mode, using external experiments to resolve degeneracies, enhancing CP violation discovery potential.

Findings

T2K can achieve maximum CP sensitivity with pure neutrino runs if octant is known.

Combining T2K with NOνA and ICAL@INO improves CP violation discovery.

Antineutrino runs are mainly useful for resolving degeneracies, not for direct CP measurement.

Abstract

The main aim of the T2K experiment in Japan is to discover CP violation in the leptonic sector by measuring the Dirac phase $\delta_{CP}$. For that purpose T2K has already started collecting data in both neutrino and antineutrino mode. But in this work we will show that, in T2K the main role of the antineutrinos is to resolve the octant degeneracy. If the octant is known then the pure neutrino run of T2K is capable to give the maximum CP sensitivity. On the other hand in the experiment like NO$\nu$A, antineutrinos are still useful even when octant is known. Thus we propose that let T2K run in the dominant neutrino mode whereas the antineutrino component of the other experiments can resolve the octant degeneracy in T2K. As an example we show that if T2K is combined with the experiments NO$\nu$A and ICAL@INO, then T2K will have the potential to discover CP violation with maximum sensitivity in the dominant neutrino mode.