Maximal ${\nu }_e$ oscillations, Borexino and smoking guns

Abstract

We examine the maximal ${\nu }_e-->{\nu }_s$ and ${\nu }_e-->{\nu }_{\mu },\tau$ oscillation solutions to the solar neutrino problem. These solutions lead to roughly a 50% solar flux reduction for the large parameter range $3\times 10^{-10}<\delta m^2/e{V}^2<10^{-3}$. It is known that the earth regeneration effect may cause a potentially large night-day asymmetry even for maximal neutrino oscillations. We investigate the night-day asymmetry predictions for the forthcoming Borexino measurement of the ^7Be neutrinos for both maximal ${\nu }_e-->{\nu }_s$ and ${\nu }_e-->{\nu }_{\mu },\tau$ oscillations. If $y\times 10^{-8}<\delta m^2/e{V}^2<4y\times 10^{-5}$ (with y = 0.5 for ${\nu }_e-->{\nu }_s$ case and y = 1 for ${\nu }_e-->{\nu }_{\mu },\tau$ case) then the maximal neutrino oscillations will lead to observable night-day asymmetries in Borexino and/or superKamiokande. With Kamland covering the high mass range, $10^{-5}<\delta m^2/e{V}^2<10^{-3}$ and Borexino/superK covering the low mass range, $3\times 10^{-10}<\delta m^2/e{V}^2<5\times 10^{-9}$ ("just so" region), essentially all of the $\delta m^2$ parameter space will soon be scrutinized.

Comments: Various improvements...still about 6 pages with some figs