Is neutrino decay really ruled out as a solution to the atmospheric neutrino problem from Super-Kamiokande data?

Abstract

In this paper we do a detailed ${\chi }^2$-analysis of the 848 days of Super-Kamiokande(SK) atmospheric neutrino data under the assumptions of ${\nu }_{\mu }-{\nu }_{\tau }$ oscillation and neutrino decay. For the latter we take the most general case of neutrinos with non-zero mixing and consider the possibilities of the unstable component in ${\nu }_{\mu }$ decaying to a state with which it mixes (scenario (a)) and to a sterile state with which it does not mix (scenario (b)). In the first case $\Delta m^2$ (mass squared difference between the two mass states which mix) has to be $>$ 0.1 $e{V}^2$ from constraints on $K$ decays while for the second case $\Delta m^2$ can be unconstrained. For case (a) $\Delta m^2$ does not enter the ${\chi }^2$-analysis while in case (b) it enters the ${\chi }^2$-analysis as an independent parameter. In scenario (a) there is \dm averaged oscillation in addition to decay and this gets ruled out at 100.0% C.L. by the latest SK data. Scenario (b) on the other hand gives a reasonably good fit to the data for \dm $\sim 0.001e{V}^2$.

Comments: Version to appear in Astropart. Phys