No abstract

A search for exclusive decays of Bt and Bf mesons has been performed in the channels Bi 4 Jq, Bz + Jq Bi 4 Jr0 and Bg -_) J.R'. The data sample consisted of more than three and half million hadronic Z decays collected by the L3 experiment at LEP from 1991 through 1995. No candidate events have been observed for any of the modes thus determining upper limits at 90% confidence level: 3.2 x low4 on Br(Bj --+ Jr') and the first experimental limits: Br(J3: -+ Jv) < 1.2 x 10w3, Br(Bt -+ 57) < 3.8 x 10p3, Br(By -+ Jr') < 1.2 X 10U3.

Using a data sample of 1475 000 Z-f q4(y) events collected during 1994 with the L3 detector at LEP, we have studied the purely leptonic decays of heavy flavour mesons, D;