Tau neutrino mass from semileptonic decays

The semileptonic three particle decays of the tau provide determinations of the tau neutrino mass. The shift of the maximal energy of the observable final state particles is linear in the neutrino mass. The endpoint energy of the pion and a partially integrated decay rate in tau → πωνsub(tau) and tau → πrhoνsub(tau) are sensitive to a neutrino mass smaller than 100 MeV. Thus, the present bound on msub(νtau) can significantly be improved. (orig.)