Direct bounds on the tau neutrino mass from LEP

Abstract

A review of direct bounds on the mass of the tau neutrino obtained at the LEP collider is presented. In addition to published results it includes preliminary results presented at recent conferences and new results presented at the 1996 Tau Workshop. The different techniques and decay modes employed by the ALEPH, DELPHI and OPAL collaborations are compared. The impact of the theoretical modelling of tau decays is also discussed. The most stringent 95% CL limit on the tau neutrino mass is now obtained by a preliminary ALEPH analysis which combines the results from τ → 5π ± (π 0 )ν τ and τ → 3π ± ν τ decays. This bound constraints the mass of the tau neutrino below 18.2 MeV/c 2 .