Study of parameter degeneracy and hierarchy sensitivity of NO ν A in presence of sterile neutrino

Abstract

The first hint of the neutrino mass hierarchy is believed to come from the long-baseline experiment NOνA. Recent results from NOνA shows a mild preference towards the CP phase δ13 ¼ −90° and normal hierarchy. Fortunately this is the favorable area of the parameter space which does not suffer from the hierarchy-δ13 degeneracy and thus NOνA can have good hierarchy sensitivity for this true combination of hierarchy and δ13. Apart from the hierarchy-δ13 degeneracy there is also the octant-δ13 degeneracy. But this does not affect the favorable parameter space of NOνA as this degeneracy can be resolved with a balanced neutrino and antineutrino run. However, if we consider the existence of a light sterile neutrino then there may be additional degeneracies which can spoil the hierarchy sensitivity of NOνA even in the favorable parameter space. In the present work we find that apart from the degeneracies mentioned above, there are additional hierarchy and octant degeneracies that appear with the new phase δ14 in the presence of a light sterile neutrino in the eV scale. In contrast to the hierarchy and octant degeneracies appearing with δ13, the parameter space for hierarchy-δ14 degeneracy is different in neutrinos and antineutrinos though the octant- δ14 degeneracy behaves similarly in neutrinos and antineutrinos. We study the effect of these degeneracies on the hierarchy sensitivity of NOνA for the true normal hierarchy.