The ATLAS Experiment is a multi-purpose detector, operating at the LHC. In this thesis the first observation of W? ? ? decays in ATLAS with proton-proton collisions at 7 TeV centre-of-mass energy is presented. The amount of data used corresponds to an integrated luminosity of 2. 46�0. 27 pb^ (? 1). The W? ? ? decays are searched in the channel in which the tau decays into a neutrino and a hadronic system.
LIDIA DELL'ASTA (Fri,) studied this question.