Testing the Pseudo-Dirac Nature of Atmospheric Neutrinos

Abstract

Pseudo-Dirac neutrinos are characterized by extremely small mass-squared differences between two nearly degenerate, strongly-mixed, active-sterile states. These differences are associated with new very-long oscillation lengths and provide a probe of the nature of neutrinos. Atmospheric neutrinos can probe these oscillations as they allow access to a broad range of baseline distances, from tens of kilometers to the Earth's diameter. We investigate the sensitivity of an experiment like the Deep Underground Neutrino Experiment (DUNE) to the pseudo-Dirac nature of neutrinos through measurements of the atmospheric neutrino flux. We concentrate on the modifications to the atmospheric neutrino energy and angular spectra induced by one new oscillation frequency associated with the $ν_3$ state and determine the parameter space that can be probed with atmospheric neutrinos at a DUNE-like detector. We also comment on the sensitivity of these measurements to the sub-leading "solar" oscillations, which are also characterized by a relatively small mass-squared difference.