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Abstract:
Recording of sub-MeV solar neutrinos (υpp,υBe7) in the Gallium Neutrino Observatory (GNO) is essential in further defining the neutrino oscillation parameters (masses, mixings). Continued error reduction is crucial in this context. The data set GNO H is now completed. The result from 43 runs (May 1998 through January 2002) is 65 ± 7 SNU. The total record is now 108 runs (65 Gallex, 43 GNO [19 GNOI, 24 GNO II]), the combined result is 71 ± 6 SNU. The systematical error in GNO is reduced to ± 3.0 SNU. This substantial error reduction has been achieved mainly through internal counter calibrations, an improved Rn-correction, and the introduction of neural network data analysis. The physics potential of future sub-MeV neutrino studies demands further efforts. Work is underway towards even better 71Ge counting efficiency by application of cryotechnics and towards a new and more precise 51Cr neutrino source experiment (>2.5 MCi) for an improved determination of the cross section for υ-capture on 71Ga.
