Top quark mass measurement using template methods, with 35 pb−1 recorded by the ATLAS detector, at sqrt(s) = 7 TeV.

A first measurement of the top quark mass (mtop) has been performed by ATLAS with the first 35 pb−1 recorded by the experiment. This measurement is based on three template methods, in the tt ̄ → lepton + jets channel. One of these methods, described in details here, makes use of the observable R32, event-by-event ratio of the reconstructed top-quark and W boson masses associ- ated to the hadronically decaying top quark candidates; combining both channels, the measured top quark mass is: mtop = (169.3±4.0stat ±4.9syst) GeV. Two additional template methods are also presented; they lead to consistent results, with different sensitivities to systematic effects.