Matter effect in presence of a sterile neutrino and resolution of the octant degeneracy using a liquid argon detector

TL;DR

This paper investigates how the presence of a sterile neutrino affects the ability of a liquid argon detector to determine the octant of the neutrino mixing angle θ23, analyzing oscillation probabilities and sensitivities.

Contribution

It provides an analytical framework for oscillation probabilities with a sterile neutrino and evaluates octant sensitivity using both beam and atmospheric neutrinos with a liquid argon detector.

Findings

Combined beam and atmospheric data improve octant sensitivity.

Sensitivity exceeds 4σ for certain true θ23 values.

Charge tagging enhances discrimination between neutrino and antineutrino events.

Abstract

Results from the experiments like LSND, and MiniBooNE hint towards the possible presence of an extra eV scale sterile neutrino. The addition of such a neutrino will significantly impact the standard three flavour neutrino oscillations; in particular, it can give rise to additional degeneracies due to new sterile parameters. In our work, we investigate how the sensitivity to determine the octant of the neutrino mixing angle $\theta_{23}$ is affected by introducing a sterile neutrino to the standard neutrino oscillation framework. We compute the oscillation probabilities in presence of a sterile neutrino, analytically, using the approximation that $\Delta_{21}$, the smallest mass squared difference, is zero. We use these probabilities to understand the degeneracies analytically at different baselines. We present our results of the sensitivity to octant of $\theta_{23}$ for beam neutrinos using a liquid argon time projection chamber (LArTPC). We also obtain octant sensitivity using atmospheric neutrinos using the same LArTPC detector without any charge identification capability. In addition, we include the charge tagging capability of muon capture in argon which allows one to differentiate between muon neutrino and antineutrino events. The combined sensitivity of beam and atmospheric neutrinos in a similar experimental setup is also delineated. We observe that by combining simulated data from the beam and atmospheric neutrinos (including charge-id for muons), the sensitivity to the octant of $\theta_{23}$ for true values of $\theta_{23}=41^\circ(49^\circ)$ exceeds $4\sigma(3\sigma)$ for more than $50\%$ values of true $\delta_{13}$.