Probing non-standard couplings of neutrinos at the Borexino detector

The present experimental status does not exclude weak-strength non-standard interactions of neutrinos with electrons. These interactions can be revealed in solar neutrino experiments. Our discussion covers several aspects related to this issue. First, we perform an analysis of the Super-Kamiokande and SNO data to investigate their sensitivity to such interactions. In particular, we show that the nu(e) oscillation into sterile neutrinos can be still allowed if nu(e) has extra interactions of the proper strength. Second, we suggest that the Borexino detector can provide good signatures for these non-standard interactions. Indeed, in Borexino the shape of the recoil electron spectrum from the nu(e) --> nu(e) scattering essentially does not depend on the solar neutrino conversion details, since most of the signal comes from the mono-energetic Be-7 neutrinos. Hence, the partial conversion of solar nu(e) into a nearly equal mixture of nu(mu) and nu(tau), as is indicated by the atmospheric neutrino data, offers the chance to test extra interactions of nu(tau), or of nu(e) itself. (C) 2002 Elsevier Science B.V. All rights reserved.