Neutrino-oscillation experiments at the Gösgen nuclear power reactor

A search for neutrino oscillations has been conducted at the 2800-MW (thermal) nuclear power reactor in G\"osgen (Switzerland), providing 510^20 electron antineutrinos per second. The energy spectrum of the antineutrinos was measured at three distances, 37. 9, 45. 9, and 64. 7 m, from the reactor core. The detection of the neutrinos is based on the reaction ₄+pe^++n. Roughly 10^4 antineutrinos were registered at each of the three measuring positions. The measured spectra are analyzed in terms of a two-neutrino oscillation model and the results are represented as exclusion plots for the oscillation parameters m^2 and sin^22theta. Two analyses are performed: Analysis A relies exclusively on the data measured at the three different distances; analysis B combines the measured data with additional information, in particular with the reactor antineutrino spectrum as derived from independent -spectroscopic measurements. Both analyses show that the data are consistent with the absence of neutrino oscillations, and rule out large regions of parameters (m^2, theta). The resulting limits on the oscillation parameters are m^20. 019 eV^2 (90% C. L. ) for maximum mixing and sin^22theta0. 21 (90% C. L. ) for m^2>5 eV^2.