Improved limits on oscillation parameters from ν_e-disappearance measurements at the Gösgen power reactor

The positron spectrum from the reaction ν_e+p→e⁺+n was measured at a distance of 64.7 m from the core of the Gösg en power reactor. These new data, combined with those of previous measurements performed under otherwise identical conditions at 37.9 m and 45.9 m, were analyzed in terms of two-neutrino oscillations of the type ν_e ↔ x. No evidence for neutrino-oscillations was found. In particular, the oscillation parameter region favored by an experiment at the Bugey reactor is not supported by the data presented here.