The Physics of antineutrinos in DUNE and resolution of octant degeneracy

Abstract

We study the proficiency of the DUNE experiment, which will be the first beam based experiment to use a baseline longer than 1000 km and a wide band flux profile, to unmask the octant of the leptonic mixing angle θ23. It has been realized, in the context of the off-axis experiments T2K and NOνA with baselines <1000 km, that combination of equal neutrino and antineutrino runs can help to resolve the octant degeneracy. In this work we examine in detail if, due to the broad-band beam and comparatively longer baseline of DUNE, the above conclusions are altered and how does that affect the octant sensitivity. We find that for the DUNE baseline of 1300 km, due to enhanced matter effect, the neutrino and antineutrino probabilities are different which creates a tension in the case of combined runs because of which (i) octant sensitivity can come from Pμμ channel, (ii) addition of antineutrinos improve octant sensitivity even in the parameter space where neutrinos do not suffer from octant degeneracy. Thus in this case the equal amount of neutrino and antineutrino run may not turn out as the optimal combination. In view of this we study the physics of antineutrinos in DUNE and investigate the best combination of neutrino-antineutrino run that is required to resolve octant degeneracy at specific confidence levels. We study this for two detector configurations -- (i) a 10 kt detector and (ii) a 34 kt detector.