Doe/er/40561-137-int94-13-02 Boron Neutrino Flux and the Msw Solution of the Solar Neutrino Problem

There are large uncertainties in the predictions of the boron neutrino ux from the Sun which cannot be considered as being of purely statistical origin. We treat the magnitude of this ux, B , as a parameter to be found from experiment. The properties of the MSW solution to the solar neutrino problem for diierent values of B are studied. Present data give the bounds: 0:38 < B = 0 B < 3:1 (2), where 0 B 5:7 10 6 cm 2 s 1 is the ux in the reference SSM. The variations of the ux in this interval enlarge the allowed region of mixing angles: sin 2 2 = 8 10 4 2 10 2 (small mixing solutions) and sin 2 2 = 0:2 0:85 (large mixing solution). If the value of the original boron neutrino ux is about that measured by Kamiokande, a consistent description of the data is achieved for sin 2 2 (0:8 2) 10 3 (\very small mixing solution"). The solution is characterized by a strong suppression of the beryllium neutrino line, a weak distortion of the high energy part of the boron neutrino spectrum and a value of the double ratio (CC=NC) exp =(CC=NC) SSM at E > 5 MeV close to 1. We comment on the possibility to measure the neutrino parameters and the original boron neutrino ux in future experiments.