Upper limit for the decay B- -> tau(-)(v)over-bar(tau) the b -> tau(v)over-bar(tau)X branching ratio

The branching ratio for the leptonic decay of charged B mesons (B- --> tau (-)<(<nu>)over bar>(tau)) has been measured using selected leptonic tau (-) --> l(-)nu (tau)<(<nu>)over bar>(l) and hadronic tau (-) --> nu X-tau decays in Z --> b (b) over bar decays recorded by DELPHI at LEP1 in 1992-1995. The result, BR(B- --> tau (-)<(<nu>)over bar>(tau)) < 1.1 x 10(-3) at the 90% confidence level, is consistent with standard model expectations and puts a constraint on the ratio tan <beta>/MH+/- < 0.46 (GeV/c(2))(-1) in the framework of models with two Higgs doublets (type II Higgs doublet model). From the missing energy distribution in Z --> b (b) over bar decays without identified leptons, the b --> tau<(<nu>)over bar>X-tau branching ratio has been measured in the hadronic channel tau --> nu X-tau'. The result, BR(b --> tau<(<nu>)over bar>X-tau) = (2.19 +/- 0.24 (stat) +/- 0.39 (syst))%, is consistent with the Standard Model prediction and with previous experimental measurements. (C) 2000 Elsevier Science B.V. All rights reserved.