Speaker
Description
Within the framework of dispersion theory we analyze the decays $\bar B_{d,s}^0 \to J/\psi M_1 M_2$ with $M_1 M_2$ being an scalar isoscalar or isovector pair of pseudoscalars, $\pi\pi$, $\bar K K$ or $\pi\eta$. In a fit of the $\bar B_{d,s}^0 \to J/\psi\pi\pi$ spectrum to data we fix several parameters, whose number is reduced significantly compared to a phenomenological analysis. Using these fit results we give predictions for the other final states, solely based on coupled-channel relations between the $\pi\pi$ and $\bar K K$ and the $\pi\eta$ and $\bar K K$ pairs, respectively, and isospin relations. These relations allow to deduce crucial information on $\pi\eta$ scattering and to compare the $f_0(980)$ vs. the $a_0(980)$ signal, which dominate the considered spectra in the isoscalar or isovector meson-pair final-states, respectively.
