A Test of the Equivalence Principle by Long-baseline Neutrino-oscillation Experiments

We show that a breakdown of the universality of the gravitational couplings to different neutrino flavors can be tested in long-baseline neutrinooscillation experiments. In particular we have analyzed in detail a proposed experiment at SOUDAN 2 with νμ beams from the Fermilab Main Injector. It turns out that we can study both masses of neutrinos and such a breakdown with sensitivity to the order of 10−14 by investigating the energy spectrum of the resulting muons.