A QCD analysis is reported of ATLAS data on inclusive $W^{\pm }$ and $Z$ boson production in $pp$ collisions at the LHC, jointly with $ep$ deep-inelastic scattering data from HERA. The ATLAS data exhibit sensitivity to the light quark sea composition and magnitude at Bjorken $x\sim 0.01$. Specifically, the data support the hypothesis of a symmetric composition of the light quark sea at low $x$. The ratio of the strange-to-down sea quark distributions is determined to be ${1.00}_{-0.28}^{+0.25}$ at absolute four-momentum transfer squared $Q^2=1.9{\mathrm{GeV}}^2$ and $x=0.023$.

• Received 19 March 2012

DOI:https://doi.org/10.1103/PhysRevLett.109.012001

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© 2012 CERN, for the ATLAS Collaboration