A model-independent analysis of final-state interactions in B ¯ d / s 0 → J / ψ π π $$ {overline{B}}_{d/s}^0to J/psi pi pi $$

Exploiting b-meson decays for standard model tests and beyond requires a precise understanding of the strong final-state interactions that can be provided model-independently by means of dispersion theory. this formalism allows one to deduce the universal pion-pion final-state interactions from the accurately known ππ phase shifts and, in the scalar sector, a coupled-channel treatment with the kaon-antikaon system. in this work an analysis of the decays $$ {overline{b}}_d^0to j/psi {pi}^{+}{pi}^{-} $$ and $$ {overline{b}}_s^0to j/psi {pi}^{+}{pi}^{-} $$ is presented. we find very good agreement with the data up to 1.05 gev in the ππ invariant mass, with a number of parameters reduced significantly compared to a phenomenological analysis. in addition, the phases of the amplitudes are correct by construction, a crucial feature for many cp violation measurements in heavy-meson decays.