We demonstrate that dispersion theory allows one to deduce crucial information on $\pi\eta$ scattering from the final-state interactions of the light mesons visible in the spectral distributions of the decays $\bar{ B}^0_d \to J/\psi(\pi^0\eta,K^+K^-,K^0\bar{ K}^0)$. 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 $\bar{ B}^0_d \to J/\psi\pi^+\pi^-$ measured recently at LHCb, letting the corresponding measurement appear feasible.
Categories: hep-ph hep-ex