Bounds on tau neutrino magnetic moment and charge radius from Super-K and SNO observations

Abstract

Neutrinos can scatter electrons in water detectors through their magnetic moments and charge radii in addition to the charged and neutral currents channels. The recent solar neutrino charged current event rates announced by SNO with the earlier solar and atmospheric neutrino observations from Super-Kamiokande allows us to put upper bounds of $\mu <10^{-9} \mu_B$ on neutrino magnetic moments and $<r^2> < 10^{-31} cm^2$ on the neutrino charge radii. For the electron and muon neutrinos these bounds are comparable with existing bounds but for tau neutrinos these bounds are three orders of magnitude more stringent than earlier terrestrial bounds. These bounds are independent of any specific model of neutrino oscillations.