A study of D∗+π− production in semileptonic B decay

n a sample of 1.5 million hadronic decays of the Z collected by the ALEPH detector, a search is carried out for the decays B → D10(2420)l−νX and B → D2∗0(2460)l−νX. The product branching ratio for D10 production is measured to be Br(b → B) × Br(B → D10l−νX) × Br(D10 → D∗+π−) = (2.04 ± 0.58stat ± 0.34syst) × 10−3, and a 95% confidence level limit of Br(b → B) × Br(B → D2∗0l−νX) × Br(D2∗0 → D∗+π−) ≤ 0.81 × 10−3 is obtained for D2∗0 production. A topological search sensitive to the processes above, but also to wide resonances that decay to D∗+π− and to non-resonant D∗+π− production is also carried out, yielding Br(b→ B) ×Br(B →D∗+π−l−νX)= (3.7 ± 1.0stat ± 0.7syst) × 10−3. Direct evidence of D∗π production inconsistent with D10 and D2∗0 in semileptonic B decay is presented.