Observation of [bar over B] → D[superscript (*)]π[superscript +]π[superscript −]ℓ[superscript −][bar over ν] Decays in e[superscript +]e[superscript −] Collisions at the Υ(4S) Resonance

Abstract

We report on measurements of the decays of [bar over B] mesons into the semileptonic final states [bar over B] → D[superscript (*)]π[superscript +]π[superscript -]ℓ[superscript -][bar over ν], where D[superscript (*)] represents a D or D[superscript *] meson and ℓ[superscript -] is an electron or a muon. These measurements are based on 471 × 10[superscript 6] B[bar over B] pairs recorded with the BABAR detector at the SLAC asymmetric B factory PEP-II. We determine the branching fraction ratios R[(*) over π[superscript +]π[superscript -]] = B([bar over B] → D[superscript (*)]π[superscript +]π[superscript -]ℓ[superscript -][bar over ν])/B([bar over B] → D[superscript (*)]ℓ[superscript -][bar over ν]) using events in which the second B meson is fully reconstructed. We find R[subscript π[superscript +]π[superscript -]] = 0.067 ± 0.010 ± 0.008 and R[* over π[superscript +]π[superscript -]] = 0.019 ± 0.005 ± 0.004, where the first uncertainty is statistical and the second is systematic. Based on these results and assuming isospin invariance, we estimate that [bar over B] → D[superscript (*)]ππℓ[superscript -][bar over ν] decays, where π denotes either a π[superscript ±] and π[superscript 0] meson, account for up to half the difference between the measured inclusive semileptonic branching fraction to charm hadrons and the corresponding sum of previously measured exclusive branching fractions.