Using 1.45 million hadronic Z decays collected by the ALEPH experiment at LEP, the 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 . These measurements are consistent with SM expectations, and put the constraint tan GeV−1 at 90% confidence level on all Type II two Higgs doublet models (such as the MSSM).