First Observation of the Decays B⁰→ D*⁻ppπ⁺ and B⁰→ D*⁻pn

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We report the first observation of exclusive decays of the type B to D* N anti-N X, where N is a nucleon. Using a sample of 9.7 times 10⁶ B-Bbar pairs collected with the CLEO detector operating at the Cornell Electron Storage Ring, we measure the branching fractions B(B⁰ → D*⁻ proton antiproton π+) = (6.5⁺¹.³₋₁.₂ +- 1.0) × 10⁻⁴ and B(B⁰ → D*⁻ proton antineutron) = (14.5⁺³.⁴₋₃.₀ +- 2.7) times 10⁻⁴. Antineutrons are identified by their annihilation in the CsI electromagnetic calorimeter.