How to employ B¯d0→J/ψπη,K¯K decays to extract information on πη scattering

A bstract We demonstrate that dispersion theory allows one to deduce crucial information on π η scattering from the final-state interactions of the light mesons visible in the spectral distributions of the decays B ¯ d 0 → J / ψ π 0 η , K + K − , K 0 K ¯ 0 . Thus high-quality measurements of these differential observables are highly desired. The corresponding rates are predicted to be of the same order of magnitude as those for B ¯ d 0 → J / ψ π + π − measured recently at LHCb, letting the corresponding measurement appear feasible.