The need for an early anti-neutrino run of NOvA

TL;DR

This paper emphasizes the importance of an early anti-neutrino run in the NOvA experiment to improve neutrino mass hierarchy determination, especially considering recent measurements of the mixing angle and degeneracies in data.

Contribution

It analyzes the hierarchy sensitivity of NOvA with early data and demonstrates that combined neutrino and anti-neutrino runs enhance hierarchy discrimination across all parameter degeneracies.

Findings

Combined $ u$ and $ar{ u}$ data improves hierarchy sensitivity.

Early anti-neutrino runs enable hierarchy determination for all octant-hierarchy combinations.

Pure neutrino data alone has limited hierarchy sensitivity due to degeneracies.

Abstract

The moderately large value of $\ty$, measured recently by reactor experiments, is very welcome news for the future neutrino experiments. In particular, the \nova experiment, with 3 years each of $\nu$ and $\anu$ runs, will be able to determine the mass hierarchy if one of the following two favourable combinations is true: normal hierarchy with $-180^\circ \leq \dcp \leq 0$ or inverted hierarchy with $0\leq \dcp \leq 180^\circ$. In this report, we study the hierarchy reach of the first 3 years of \nova data. Since $\sin^2 2 \tz$ is measured to be non-maximal, $\tz$ can be either in the lower or higher octant. Pure $\nu$ data is affected by $\ty$-hierarchy and octant-hierarchy degeneracies, which limit the hierarchy sensitivity of such data. A combination of $\nu$ and $\anu$ data is not subject to these degeneracies and hence has much better hierarchy discrimination capability. We find that, with a 3 year $\nu$ run, hierarchy determination is possible for only two of the four octant-hierarchy combinations. Equal 1.5 year runs in $\nu$ and $\anu$ modes give good hierarchy sensitivity for all the four combinations.