Experimental tests of lepton universality inτdecay

The branching fractions for τ→eνν_τ, μνν_τ, and hν_τ are measured using data collected with the CLEO detector at the CESR e⁺e^- collider: Bₑ=0.1776±0.0006±0.0017, B_μ=0.1737±0.0008±0.0018, and Bₕ=0.1152±0.0005±0.0012, where the first error is statistical, the second systematic, and h refers to either a charged π or K. Also measured is the τ mass, m_τ=(1778.2±1.4) MeV. Lepton universality is affirmed by the relative branching fractions (B_μ/Bₑ=0.9777±0.0063±0.0087, Bₕ/Bₑ=0.6484±0.0041±0.0060) and the charged-current gauge coupling-constant ratios (g_μ/gₑ=1.0026±0.0055, g_τ/g_μ=0.9990±0.0098). The τ mass result may be recast as a τ neutrino mass limit, m_ν_τ<60 MeV at 95% C.L.