This Letter reports a measurement of the muon charge asymmetry from W bosons produced in proton-proton collisions at a centre-of-mass energy of 7 TeV with the ATLAS experiment at the LHC. The asymmetry is measured in the W -} mu nu decay mode as a function of the muon pseudorapidity using a data sample corresponding to a total integrated luminosity of 31 pb(-1).
The results are compared to predictions based on next-to-leading order calculations with various parton distribution functions. This measurement provides information on the u and d quark momentum fractions in the proton. (C) 2011 CERN.
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