A redetermination of the neutrino mass-squared difference in tri-maximal mixing with terrestrial matter effects

We re-fit for the neutrino mass-squared difference Δm2 in the threefold maximal (i.e. tri-maximal) mixing scenario using recent CHOOZ and SUPER-K data, taking account of matter effects in the Earth. While matter effects have little influence on reactor experiments and proposed long-baseline accelerator experiments with L ≲ 1000 km, they are highly significant for atmospheric experiments, suppressing naturally νe mixing and enhancing νμ−ντ mixing, so as to effectively remove the experimental distinction between threefold maximal and twofold maximal νμ−ντ mixing. Threefold maximal mixing is fully consistent with the CHOOZ and SUPER-K data and the best-fit value for the neutrino mass-squared difference is Δm2≃(0.98±0.300.23)×10−3 eV2.