Measurement of the

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 $$4.6~\hbox {fb}^{-1}$$ of integrated luminosity. The selected data sample consists of $$7.8\times 10^6$$ candidates in the $$W\rightarrow \mu \nu $$ channel and $$5.9\times 10^6$$ candidates in the $$W\rightarrow e \nu $$ 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 $$\begin{aligned} \nonumber m_W = 80370&\pm 7~(\text {stat.}) \pm 11 (\text {exp. syst.}) \\&\pm 14~(\text {mod. syst.})~\text {MeV} \\ = 80370&\pm 19\,\text {MeV}, \end{aligned}$$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 $$m_{W^+}-m_{W^-} = -\,29 \pm 28$$ MeV