A search for neutrino oscillations by measurement of the νe spectra at two distances from a nuclear reactor

Abstract The positron spectrum from the reaction ν e + p → e + + n has been measured at L = 45.9 m from the core of the Gosgen power reactor. The data, combined with those of our previous measurement at 37.9 m, are analysed in terms of two-neutrino oscillations of the type ν e ↔ x . This analysis is essentially independent of external data on the spectral distribution of reactor neutrinos. No evidence for neutrino oscillations was found. A comprehensive analysis including data on the spectral distribution yields upper limits for the oscillation parameters of Δm 2 ⩽ 0.016 eV 2 (90% CL for full mixing, and sin 2 2 θ ⩽ 0.16 (90% CL) for large Δm 2 .