Measurement of D^-_s→τ^-ν̅_τ and a new limit for B^- →τ⁻ν̅_τ

Abstract

Using a data sample of 1 475 000 Z → qq̅(γ) events collected during 1994 with the L3 detector at LEP, we have studied the purely leptonic decays of heavy flavour mesons, D⁻_s→τ⁻ν̅_τ and a new limit for B⁻ →τ⁻ν̅_τ. A signal is observed in the invariant mass distribution M(γD_s⁻) corresponding to the decay sequence D^∗−→γD_s⁻, D_s⁻→τ⁻ν̅_τ, τ⁻_τ, τ⁻ →l⁻ν→₁ν_τ. The branching fraction for D_s⁻→τ⁻ν̅_τ decays is measured to be β(_s⁻→τ⁻ν̅_Τ) = 0.074 ± 0.028(stat) ± 0.016(syst) ±0.018(norm0. No signal of B⁻→τ⁻ν̅_τ decays is observed in the data, corresponding to an upper limit on the branching franction β (B⁻→τ⁻ν̅_τ) < 5.7 x 10^-4 at 90% CL.