Nonmaximal ${\theta }_{23}$ mixing at NOvA from neutrino decoherence

Abstract

In study of muon neutrino disappearance at 810 km, the NOvA experiment finds flavor mixing of the atmospheric sector to deviate from maximal (${\sin }^2{\theta }_{23}=0.5$) by 2.6 $\sigma$. The result is in tension with the 295-km baseline measurements of T2K which are consistent with maximal mixing. We propose that ${\theta }_{23}$ is in fact maximal, and that the disagreement is harbinger of environmentally-induced decoherence. The departure from maximal mixing can be accounted for by an energy-independent decoherence of strength $\Gamma =(2.3\pm 1.1)\times 10^{-23}$ GeV.

Comments: 5 pages, 2 figures, accepted for publication in Physical Review Letters