Measurements of BR(b → τ-ν̄τX) and BR(b → τ-ν̄τD*±X) and upper limits on BR(B- → τ-ν̄τ) and BR(b → sνν̄)

Inclusive branching ratios involving b → τ transitions are measured in approximately four million hadronic Z decays collected by the ALEPH detector at LEP. The fully-inclusive branching ratio BR(b → τ-ν̄τX) and the semi-inclusive branching ratio BR(b → τ-ν̄τD*±X) are measured to be (2.43 ± 0.20 ± 0.25)% and (0.88 ± 0.31 ± 0.28)%, in agreement with the standard model predictions. Upper limits on the branching fractions BR(B- → τ-v̄τ) and BR(b → sνν̄) are set to 8.3 × 10-4 and 6.4 × 10-4 at the 90% C.L. These results allow a 90% C.L. lower limit of 0.40 (GeV/c2)-1 to be set on the tan β/mH± ratio, in the framework of type-II two-Higgs-doublet models.