A limit on the mass of the ντ

Abstract A limit on the mass of the tau neutrino m ν τ is derived from 4.5×10 6 tau pairs produced in an integrated luminosity of 5.0 fb −1 of e + e − →γ∗→τ + τ − reactions at center of mass energies ≈ 10.6 GeV. The measurement technique involves a two-dimensional extended likelihood analysis, including the dependence of the end-point population on m ν τ , and allows for the first time an explicit background contribution. We use the the decays τ →5 πν τ and τ →3 π 2 π 0 ν τ to obtain an upper limit of 30 MeV/ c 2 at 95% C.L.