A COHERENT enlightenment of the neutrino Dark Side

Understand

In the presence of non-standard neutrino interactions (NSI), oscillation data are affected by a degeneracy which allows the solar mixing angle to be in the second octant (aka the dark side) and implies a sign flip of the atmospheric mass-squared difference.

• This leads to an ambiguity in the determination of the ordering of neutrino masses, one of the main goals of the current and future experimental neutrino program.
• We show that the recent observation of coherent neutrino--nucleus scattering by the COHERENT experiment, in combination with global oscillation data, excludes the NSI degeneracy at the $3.1\sigma$ ($3.6\sigma$) CL for NSI with up (down) quarks.