Measurement of the b → τ- ν -τX branching ratio and an upper limit on B- → τ- ν -τ

Using 1.45 million hadronic Z decays collected by the ALEPH experiment at LEP, the b → τ- ν -τX branching ratio is measured to be 2.75 ± 0.30 ± 0.37%. In addition an upper limit of 1.8 × 10-3 at 90% confidence level is placed upon the exclusive branching ratio of B- → τ- ν -τ. These measurements are consistent with SM expectations, and put the constraint tan β Mh < 0.52 GeV-1 at 90% confidence level on all Type II two Higgs doublet models (such as the MSSM). © 1995.