A SEARCH FOR UNCONVENTIONAL TAU DECAYS AND MEASUREMENT OF THE TAU PRODUCTION CROSS SECTION IN e+e- ANNIHILATIONS AT SPEAR*

ble present the results of an experimental study of two properties of the tau lepton performed with the MARK II detector in the SPEAR e+estorage ring at SLAC. The tau production cross section in e+eannihilation between 3.85 and 6.85 Gev in the center of mass has been measured using e-u events, and is consistent with the spin l/2, point cross section. The branching ratio product for the electron and muon leptonic decay modes is measured to be .032?.002?.004. Searches for 12 neutrinoless decay modes of the tau which violate lepton number conservation have been made. No evidence for lepton number violation is observed, and we set upper limits (90% C.L.) on the branching ratio for each decay mode. The branching ratio limit on the radiative decays r-q?’ and r+er are .055% and .064% respectively. For the 3 charged lepton decays r+eee, r+eup, r-qee, and r+upp, the branching ratio limits are .040%, .033%, .044%, and .049% respectively. Upper limits on the branching ratios are also set for the following charged lepton+neutral hadron decays of the tau: r+ep (.037%), ?-+p (.044%), r+eK” (.13%), 7+uK” (.lO%), r-+es” (.21%), and ?+a0 (.082%).