A search for lepton flavour violating τ decays at OPAL

An analysis is presented reporting on a search for non-Standard Model τ decays that violate the conservation of lepton flavour in the OPAL data 1990-1994. The modern theory of particle physics (the Standard Model) is reviewed, its successes and limitations are discussed. Theories contending for the place of successor to the Standard Model are also reviewed and their advantages and disadvantages are discussed. Special emphasis is placed on theories that predict lepton flavour violation in τ decay. A search for lepton flavour violating τ decays at OPAL is described in detail. No candidates are found, leading to an upper limit on the branching ratio Br(τ → lll) ≤ 3.2 x 10-5. Other experimental measurements, from CLEO and ARGUS, of the branching ratio of τ decay to three charged leptons are reviewed and compared. (author)