A STUDY OF D-ASTERISK+PI(-)-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) over bar --> D-1(0)(2420)l(-)<(nu)over bar>X and (B) over bar --> D-2(*0)(2460)l(-)<(nu)over bar>X. The product branching ratio for D-1(0) production is measured to be Br(b --> (B) over bar) x Br((B) over bar --> D(1)(0)l(-)<(nu)over bar>X) x Br(D-1(0) --> D-*+<pi(-)) = (2.04 +/- 0.58(stat)+/- 0.34(syst) x 10 (-3), and a 95% confidence level limit of Br(b --> (B) over bar) x Br((B) over bar --> D(2)(*0)l(-)<(nu)over bar>X) x Br(D-2(*0) --> D(*+)pi(-)) less than or equal to less than or equal to 0.81 X 10(-3) is obtained for D-2(*0) production. A topological search sensitive to the processes above, but also to wide resonances that decay to D(*+)pi(-) and to non-resonant D(*+)pi(-) production is also carried out, yielding Br(b--> (B) over bar B) xBr((B) over bar -->D(*+)pi(-) l(-)<(nu)over bar>X>)= (3.7 +/- 1.0(stat) +/- 0.7(syst)) x 10(-3). Direct evidence of D(*)pi production inconsistent with D-1(0) and D-2(*0) in semileptonic B decay is presented.