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

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-flavor 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 θ23 is affected by introducing a sterile neutrino to the standard three generation framework. We compute the oscillation probabilities analytically in the presence of a sterile neutrino, using the approximation that Δ21, 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 θ23 for beam neutrinos using a liquid argon time projection chamber (LArTPC). We also obtain octant sensitivity using atmospheric neutrinos using the same LArTPC detector. For the latter, we present our results assuming (i) no charge identification capability, and (ii) partial charge identification capability using the charge tagging ability of muon capture in argon. 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 θ23 for true values of θ23 = 41°(49°) exceeds 4σ(3σ) for more than 50% values of true δ13.