Can the hint of $\delta_{CP}$ from T2K also indicate the hierarchy and octant ?

TL;DR

This paper investigates whether the hint of $\, ext{CP}$ violation from T2K neutrino data can also reveal the neutrino mass hierarchy and octant of $ heta_{23}$, depending on the mode of T2K operation.

Contribution

It analyzes how T2K's neutrino and anti-neutrino run configurations can simultaneously constrain the hierarchy and octant given a $\, ext{CP}$ hint.

Findings

Neutrino-only mode with full exposure suggests normal hierarchy and higher octant.

Equal neutrino and anti-neutrino runs confirm normal hierarchy but leave octant undetermined.

Anti-neutrino runs influence the CP sensitivity of T2K.

Abstract

The T2K neutrino data has already given a hint for the best-fit value of the leptonic CP phase $\delta_{CP}$ as $-90^\circ$. In this paper we ask the question that if this hint is confirmed by the subsequent neutrino and anti-neutrino runs of T2K, then can it also give any information about the other two remaining unknown oscillation parameters - the neutrino mass hierarchy and octant of $\theta_{23}$. We find that if T2K runs in only neutrino mode with its full targeted exposure, then $\delta_{CP} = -90^\circ$ would indicate the true hierarchy as normal and the true octant as higher. On the other hand if T2K runs in equal neutrino and anti-neutrino mode then the true hierarchy can be confirmed as normal but the octant will remain undetermined. We have also studied the effect of anti-neutrino runs on CP sensitivity of T2K.