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

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 ?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 ?21, the smallest mass squared difference, is zero. We use these probabilities to understand analytically the degeneracies at different baselines. In our work, we investigate in the context of the DUNE experiment, the sensitivity to determine the octant of ?23 for 3+1 framework. We present our results of the sensitivity to octant of ?23 for beam neutrinos using a liquid argon time projection chamber (LArTPC) at the DUNE far detector. We also obtain octant sensitivity using atmospheric neutrinos at DUNE using a LArTPC detector without any charge identification capability. In addition, we obtain the octant sensitivity including the charge tagging capability of muon capture in argon which allows differentiating between muon neutrino and antineutrino events. The combined sensitivity of beam and atmospheric neutrinos in DUNE 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 ?23 for true values of ?23=41?(49?) exceeds 4?(3?) for more than 50% values of true ?13.