  A search is presented for charge-asymmetric production of a W' boson that has
been proposed to accommodate the forward-backward asymmetry observed in the
production of top-antitop quark pairs at the Tevatron. The new heavy W' boson
would be produced in association with a top quark and would decay into top and
down quarks. The data correspond to an integrated luminosity of 5.0 inverse
femtobarns in pp collisions at a center-of-mass energy of 7 TeV, recorded by
the CMS detector at the LHC. No significant excess above the standard model
expectations is observed, and, from a combination of the electron-plus-jets and
muon-plus-jets channels, a 95% confidence level lower limit of 840 GeV is set
on the W' boson mass for a W' boson model with values for coupling constants to
top and down quarks g(L) = 0 and g(R) = 2. In addition, a kinematic
reconstruction of the W' resonance mass using the inherent charge asymmetry of
this model finds no indication of the presence of W' events in the data.
