Events with large missing transverse energy at the cern collider: I.W→τν decay and test of τμe universality at Q2=mw2

Abstract We report results based on a sample of events with large missing transverse energy corresponding to 715 nb −n of data from the UA1 experimentat the CERN proton- antiprotoncollider. High transverse-momentum tau-leptons from W decays are observed for the first time through their semi-hadronic decay modes and associated missing transverse energy. The measured relative rates of W→e ν , W→ μν , and W→ τν provide the first direct tests of the electron-muon-tau universality of the weak charged couplings at Q 2 = m w 2 . We determine g τ g e =1.01±0.09±0.05 and g μ g e =1.05±0.07±0.08 .