Soft pion emission in semileptonicB-meson decays

An analysis of semileptonic decays of B mesons with the emission of a single soft pion is presented in the framework of the heavy-quark limit, using an effective Lagrangian which implements chiral and heavy-quark symmetries. The analysis is performed at leading order of the chrial and inverse heavy mass expansions. In addition to the ground-state heavy mesons, some of their resonances are included. The estimates of the various effective coupling constants and form factors needed in the analysis are obtained using a chiral quark model. An analysis of the decay spectrum in the squared invariant mass of the π${\mathit{D}}^{\left(\mathrm{*}\right)}$ is carried out, showing the main effects of including the resonances. As the main result, a clear indication is found that the $0^{+}$ and $1^{+}$ resonances substantially affect the rate of the decay mode with a ${\mathit{D}}^{\mathrm{*}}$ in the final state, while a less dramatic effect is also noticed in the D mode. A peak related to the $0^{\mathrm{-}}$ and $1^{\mathrm{-}}$ radially excited D mesons is clear. The obtained rates show promising prospects for studies of soft pion emission in semileptonic B-meson decays in a B-meson factory where, modulo experimental cuts, about ${10}^5$ such decays in the D meson mode and ${10}^4$ in the ${\mathit{D}}^{\mathrm{*}}$ mode could be observed per year.