Measurement of the τ topological branching ratios at LEP

The inclusive branching ratios of the τ lepton to one, three and five charged particle final states are measured from data collected with the OPAL detector at LEP. The data sample consists of 12707e+e− → τ+τ− candidate events and has an estimated background of 1.9%. The branching ratios are obtained from a simultaneous fit to the data which gives B1 = 84.48 ± 0.27 (stat) ±0.23 (sys)%, B3 = 15.26±0.26±0.22% and B5 = 0.26±0.06±0.05% respectively where B1 + B3 + B5 is constrained to equal one. The inclusive one-prong branching ratio is found to be significantly lower than the 1990 Particle Data Group world average while the branching ratio to three charged particles is correspondingly higher. The five-prong branching ratio is in agreement with the world average measurement.