  A model-independent search for the production of heavy resonances decaying
into top-antitop quark pairs is presented. The search is based on events
containing one lepton (muon or electron) and at least two jets selected from
data samples corresponding to an integrated luminosity of 4.4-5.0 inverse
femtobarns collected in pp collisions at sqrt(s) = 7 TeV. Results are presented
from the combination of two dedicated searches optimized for boosted production
and production at threshold. No excess of events is observed over the expected
yield from the standard model processes. Topcolor Z' bosons with narrow (wide)
width are excluded at 95% confidence level for masses below 1.49 (2.04) TeV and
an upper limit of 0.3 (1.3) pb or lower is set on the production cross section
times branching fraction for resonance masses above 1 TeV. Kaluza-Klein
excitations of a gluon with masses below 1.82 TeV (at 95% confidence level) in
the Randall-Sundrum model are also excluded, and an upper limit of 0.7 pb or
lower is set on the production cross section times branching fraction for
resonance masses above 1 TeV.
