Mass ordering sum rule for the neutrino disappearance channels in T2K, NOvA, and JUNO

Abstract

We revisit, reformulate, and extend a method for determining the neutrino mass ordering by using precision measurements of the atmospheric Δm2 s in both electron and muon neutrino disappearance channels, first proposed by the authors in 2005 [H. Nunokawa, Phys. Rev. D 72, 013009 (2005)PRVDAQ1550-799810.1103/PhysRevD.72.013009]. The mass ordering is a very important outstanding question for our understanding of the elusive neutrino and determination of the mass ordering has consequences to particle physics, nuclear physics, and cosmology. The JUNO reactor experiment will start data taking this year, and the precision of the atmospheric Δm2 s from electron antineutrino measurements will improve by a factor of 3 from Daya Bay's 2.4% to 0.8% within a year. This measurement, when combined with the atmospheric Δm2's measurements from T2K and NOvA for muon neutrino disappearance, will contribute substantially to the Δχ2 between the two remaining neutrino mass orderings. In this paper we derive for the first time a mass ordering sum rule that can be used to address the possibility that JUNO's atmospheric Δm2's measurement, when combined with other experiments in particular T2K and NOvA, can determine the neutrino mass ordering at the 3σ confidence level within one year of operation. For a confidence level of 5σ in a single experiment, we will have to wait until the middle of the next decade when the DUNE experiment is operating.