Search for lepton-number and lepton-flavour violation in tau decays

Abstract We have searched for neutrinoless tau decays into three charged particles as evidence for lepton-flavour or lepton-number violation. The data were collected using the ARGUS detector at the DORIS II storage ring. Tau pairs were produced by e + e − annhilation at centre-of-mass energies near 10 GeV. No evidence for lepton-number or lepton-flavour violation was observed, but the upper limits obtained are an order of magnitude lower than those previously published.