Measurement of the W-Boson Mass in pp Collisions at √s=7 TeV with the ATLAS Detector

A measurement of the mass of the W boson is presented based on proton-proton collision data recorded in 2011 at a centre-of-mass energy of 7 TeV with the ATLAS detector at the LHC, and corresponding to 4.6 fb⁻¹ of integrated luminosity. The selected data sample consists of 7.8 x 10⁶ candidates in the W → μν channel and 5.9 x 10⁶ candidates in the W → eν channel. The W-boson mass is obtained from template fits to the reconstructed distributions of the charged lepton transverse momentum and of the W boson transverse mass in the electron and muon decay channels, yielding m_w = 80370 ± 7 (stat.) ± 11(exp. syst.) ± 14 (mod. syst.) MeV = 80370 ± 19 MeV, where the first uncertainty is statistical, the second corresponds to the experimental systematic uncertainty, and the third to the physics-modelling systematic uncertainty. A measurement of the mass difference between the W⁺ and W⁻ bosons yields m_{W+} - m_{W⁻} = -29 ± 28 MeV.