A study of D*+π- production in semileptonic B decay

In 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 → D1 0(2420)l-νX and B → D2 *0(2460)l-νX. The product branching ratio for D1 0 production is measured to be Br(b → B) × Br(B → D1 0l-νX) × Br(D1 0 → 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 D1 0 and D2 *0 in semileptonic B decay is presented.