Solar neutrinos and 1-3 leptonic mixing

Abstract

Effects of the 1-3 leptonic mixing on the solar neutrino observables are studied and the signatures of non-zero $θ_{13}$ are identified. For this we have re-derived the formula for $3ν$-survival probability including all relevant corrections and constructed the iso-contours of observables in the $\sin^2 θ_{12} - \sin^2 θ_{13}$ plane. Analysis of the solar neutrino data gives $\sin^2θ_{13} = 0.007^{+ 0.080}_{-0.007}$ (90% C.L.) for $Δm^2 = 8 \cdot 10^{-5}$ eV$^2$. The combination of the ratio CC/NC at SNO and gallium production rate selects $\sin^2θ_{13} = 0.017 \pm 0.026$ ($1σ$). The global fit of all oscillation data leads to zero best value of $\sin^2 θ_{13}$. The sensitivity ($1σ$ error) of future solar neutrino studies to $\sin^2 θ_{13}$ can be improved down to 0.01 - 0.02 by precise measurements of the pp-neutrino flux and the CC/NC ratio as well as spectrum distortion at high ($E > 4$ MeV) energies. Combination of experimental results sensitive to the low and high energy parts of the solar neutrino spectrum resolves the degeneracy of angles $θ_{13}$ and $θ_{12}$. Comparison of $\sin^2 θ_{13}$ as well as $\sin^2 θ_{12}$ measured in the solar neutrinos and in the reactor/accelerator experiments may reveal new effects which can not be seen otherwise.