Measurement of the topological and hadronic decay branching fractions of the tau lepton with the L3 detector at LEP

Abstract

Using the data collected with the L3 detector at LEP during 1992–1995 run at the Z 0 peak, corresponding to an integrated luminosity of 92.63 pb −1, the topological and hadronic τ decay branching fractions are measured. Photon conversion, fake photon and backlash tracks are studied and rejected in the analysis. The decay channels are identified using a set of neural networks. The topological τ decay branching fractions are B(τ → 1-prong) = 85.14 ± 0.27 ± 0.17%, B(τ →3-prong) = 14.63 ± 0.13 ± 0.10% and B(τ → 5-prong) = 0.23 ± 0.01 ± 0.05%. The branching fractions of τ hadronic decays are determined: BR(τ → hν)=(12.51 ± 0.12 ± 0.13)%, BR(τ → hπ 0ν)=(25.38±0.18±0.14)% ,BR(τ → h2π 0ν)=(8.98±0.21±0.19)%, BR(τ → h ≥ 3π 0ν)=(1.77±0.14±0.15)% ,BR(τ → 3 hν)=(9.11 ± 0.15 ± 0.08)% ,BR(τ → 3 hπ 0ν)=(4.77 ± 0.19 ± 0.10)% ,BR(τ → 3 h ≥ 2π 0ν)=(0.45 ± 0.10 ± 0.11)%, where the first error is statistical and the second systematic.