Production of orbitally excited charm mesons in semileptonic B decays

A sample of 3.6 million hadronic Z decays recorded between 1991 and 1995 with the ALEPH detector at LEP is used to investigate semileptonic decays of B mesons into final states involving orbitally excited charm mesons. Topological vertex criteria are used to search for decays involving narrow D states as well as wide D resonances and non-resonant D() final states. The sum of the branching ratios for these processes is measured to be \begin{eqnarray*} \lefteqn{{\mathrm{Br}}({\overline {\mathrm{B}}} \to {\mathrm{D}}\pi\ell^-\overline\nu) +{\mathrm{Br}}({\overline {\mathrm{B}}} \to {\mathrm{D}}^*\pi\ell^-\overline\nu)}\\ & & = (2.26\pm 0.29(\mathrm{stat}) \pm 0.33(\mathrm{syst}))\%, \end{eqnarray*} which accounts for a significant fraction of the deficit between inclusive measurements and the sum of exclusive semileptonic B decay modes.