Data collected with the DELPHI detector from 1993 to 1995 combined with previous DELPHI results for data from 1991 and 1992 yield the branching fractions B(τ→\rm eννˉ)=(17.877±0.109stat±0.110sys)% and B(τ→μννˉ)=(17.325±0.095stat±0.077sys)% .
Abreu, P., Cortina Gil, E., DELPHI Collaboration, & et al. (1999). Measurements of the leptonic branching fractions of the tau. European Physical Journal C. Particles and Fields. https://doi.org/10.1007/s100520050583