Generalized mass ordering degeneracy in neutrino oscillation experiments

Abstract

We consider the impact of neutral-current (NC) non-standard neutrino interactions (NSI) on the determination of the neutrino mass ordering. We show that in presence of NSI there is an exact degeneracy which makes it impossible to determine the neutrino mass ordering and the octant of the solar mixing angle θ12 at oscillation experiments. The degeneracy holds at the probability level and for arbitrary matter density profiles, and hence, solar, atmospheric, reactor, and accelerator neutrino experiments are affected simultaneously. The degeneracy requires order-one corrections from NSI to the NC neutrino-quark interaction and can be tested in neutrino-nucleus NC scattering experiments.

COHERENT enlightenment of the neutrino dark side

“…This degeneracy involves not only the octant of θ 12 but also a change in sign of the larger neutrino mass-squared difference, ∆m 2 31 , which is used to parameterize the type of neutrino mass ordering (normal versus inverted). Hence, the LMA-D degeneracy makes it impossible to determine the neutrino mass ordering by oscillation experiments [10], and therefore jeopardizes one of the main goals of the upcoming neutrino oscillation program. As discussed in Refs.…”

“…This was first observed in the context of solar neutrinos, where for suitable NSI the data can be explained by a mixing angle θ 12 in the second octant, the so-called LMA-Dark (LMA-D) [5] solution. This is in sharp contrast to the established standard MSW solution [2,6], which requires a mixing angle θ 12 in the first octant.The origin of the LMA-D solution is a degeneracy in oscillation probabilities due to a symmetry of the Hamiltonian describing neutrino evolution in the presence of NSI [7][8][9][10]. This degeneracy involves not only the octant of θ 12 but also a change in sign of the larger neutrino mass-squared difference, ∆m 2 31 , which is used to parameterize the type of neutrino mass ordering (normal versus inverted).…”

“…The origin of the LMA-D solution is a degeneracy in oscillation probabilities due to a symmetry of the Hamiltonian describing neutrino evolution in the presence of NSI [7][8][9][10]. This degeneracy involves not only the octant of θ 12 but also a change in sign of the larger neutrino mass-squared difference, ∆m 2 31 , which is used to parameterize the type of neutrino mass ordering (normal versus inverted).…”

“…As discussed in Refs. [5,[10][11][12], non-oscillation data (such as that from neutrino scattering experiments) is needed to break this degeneracy.Recently, coherent neutrino-nucleus scattering has been observed for the first time by the COHERENT experiment [13], using neutrinos produced at the Spallation Neutron Source (SNS) in Oak Ridge National Laboratory. The observed interaction rate is in good agreement with the Standard Model (SM) prediction and can be used to constrain NSI.…”

“…As discussed in Refs. [5,[10][11][12], non-oscillation data (such as that from neutrino scattering experiments) is needed to break this degeneracy.…”