Barate, R (reprint author), CNRS, PHYS PARTICULES LAB, IN2P3, F-74019 ANNECY LE VIEUX, FRANCE.
A search for the B-c meson decaying into the channels J/psi pi(+) and J/psi l(+)nu(l) (l = e or mu) is performed in a sample of 3.9 million hadronic Z decays collected by the ALEPH detector. This search results in the observation of 0 and 2 candidates in each of these channels, respectively, while 0.44 and 0.81 background events are expected. The following 90% confidence level upper limits are derived: Br(Z --> BcX)/Br(Z --> q (q) over bar BR(B-c(+) --> J/psi pi(+)) < 3.6 x 10(-5), Br(Z --> BcX)/Br(Z-->q (q) over bar)Br(B-c(+) --> J/psi l(+)nu) < 5.2 x 10(-5). Another B-c(+) --> J/psi(e(+)e(-))mu(+)nu(mu) candidate with very low background probability, found in an independent analysis, is also described in detail. (C) 1997 Published by Elsevier Science B.V.