  A multivariate likelihood method to measure electroweak couplings with the
Drell-Yan process at the LHC is presented. The process is described by the
dilepton rapidity, invariant mass, and decay angle distributions. The decay
angle ambiguity due to the unknown assignment of the scattered constituent
quark and antiquark to the two protons in a collision is resolved statistically
using correlations between the observables. The method is applied to a sample
of dimuon events from proton-proton collisions at sqrt(s) = 7 TeV collected by
the CMS experiment at the LHC, corresponding to an integrated luminosity of 1.1
inverse femtobarns. From the dominant u-ubar, d-dbar to gamma*/Z to opposite
sign dimuons process, the effective weak mixing angle parameter is measured to
be sin^2(theta[eff]) = 0.2287 +/- 0.0020 (stat.) +/- 0.0025 (syst.). This
result is consistent with measurements from other processes, as expected within
the standard model.
