A search for neutrino oscillations has been conducted at the 2800-MW (thermal) nuclear power reactor in Gosgen (Switzerland), providing 5 x loz0 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 Te +p-e + +n. Roughly lo4 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 Am and sin226. 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 P-spectroscopic measurements. Both analyses show that the data are consistent with the absence of neutrino oscillations, and rule out large regions of parameters (Am 2,0). The resulting limits on the oscillation parameters are a m 2 <0.019 eV2 (90% C.L.) for maximum mixing and sin220 < 0.2 1 (90% C.L.) for Am * > 5 ev2.

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