Matter versus vacuum oscillations at long-baseline accelerator neutrino experiments
Abstract
The neutrino oscillation probabilities at the long-baseline accelerator neutrino experiments are expected to be modified by matter effects. We search for evidence of such modification in the data of T2K and NOνA, by fitting the data to the hypothesis of (a) matter modified oscillations and (b) vacuum oscillations. We find that vacuum oscillations provide as good a fit to the data as matter modified oscillations. Even extended runs of T2K and NOνA, with five years in neutrino mode (5ν) and five years in anti-neutrino mode (5ˉν), cannot make a 3σ distinction between vacuum and matter modified oscillations. The future experiment DUNE, with neutrino and anti-neutrino runs of five years each (5ν+5ˉν), can rule out vacuum oscillations by itself at 5σ if the hierarchy is normal. If the hierarchy is inverted, a 5σ discrimination against vacuum oscillations requires the combination of (5ν+5ˉν) runs of T2K, NOνA and DUNE.
