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 Delta m(2) 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 less than or similar to 1000 km, they an highly significant for atmospheric experiments, suppressing naturally nu(e) mixing and enhancing nu(mu)- nu(tau) mixing, so as to effectively remove the experimental distinction between threefold maximal and twofold maximal nu(mu)- nu(tau) 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 Delta m(2) similar or equal to (0.98 +/- (0.30)(0.23)) X 10(-3) eV(2). (C) 1999 Published by Elsevier Science B.V. All rights reserved.