Wednesday 16 June 2010

Speaker:   Prof. Gianpaolo Bellini   (Physics Department, Milan University)

Title:     Study of the neutrino interactions at a few MeV of energy, with Borexino

Abstract:

The Borexino detector has been designed to study the solar neutrinos fluxes below 1 MeV. This goal has been
achieved due to the unprecedented very low radioactive background, reached by means of various techniques
developed during 5 years of R&D.

The first results concern the solar neutrino flux from 7Be at 0.862 MeV. This determination constraints also
the limits for the pp neutrino flux, giving two reliable experimental measurements, which would validate the
present neutrino oscillation model in the vacuum regime. After a long campaign of calibrations the total error
for the 7Be neutrino flux is strongly reduced.

In addition Borexino has measured the neutrino flux from 8B with a lower threshold down to 3 MeV.

In the meantime Borexino obtained the first real evidence of antineutrinos coming from the Earth. By exploiting
its very low background and the low flux of antineutrino from reactors, as it is at the Gran Sasso site,
Borexino succeeded to reach an observation of geo-neutrinos at 4.2 sigma.

In addition the Borexino data achieved the best limits for the non Paulian transitions and for the presence of
antineutrinos in the solar neutrinos flux.

The direct measurement of the solar neutrino fluxes from pp and pep reactions is under study.