| Sumario: | This paper describes an analysis of the angular distribution of W→eν and W→μν decays, using data from pp collisions at √s =7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb -1 . Using the decay lepton transverse momentum and the missing transverse momentum, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f 0 , f L and f R over two ranges of W transverse momentum (p W T ): 35 < p W T < 50 GeV and p W T > 50 GeV. Good agreement is found with theoretical predictions. For p W T >50 GeV, the values of f 0 and f L -f R , averaged over charge and lepton flavour, are measured to be: f 0 =0. 127±0. 030±0. 108 and f L -f R =0. 252±0. 017±0. 030, where the first uncertainties are statistical, and the second include all systematic effects. © 2012 CERN for the benefit of the ATLAS collaboration.
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