Why the pseudoscalar-meson mixing angle is - 10°

Abstract

We propose a simple approach to the problem of mixing in nonets which leads to an understanding of the nature of both the "ideal" mixing angle of 35° found for the vector and tensor mesons and the "nonideal" mixing angle of - 10° found for the pseudoscalar mesons. We argue that the pseudoscalar meson mixing angle is "nonideal" because of a near degeneracy in the masses of the strange and nonstrange pseudoscalar mesons. As by-products we predict that more massive nonets will be nearly ideal and that, if charmed quarks "exist," the low-lying charm-anticharm mesons will be very narrow.