Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at √s = 7\ TeV with the ATLAS experiment

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 (pTW ): 35 < pTW< 50\ GeV and pTW> 50\ GeV . Good agreement is found with theoretical predictions. For pTW> 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.