Finite-width effects in top quark production at hadron colliders

Production cross sections for $t\overline{t}$ and $t\overline{t}j$ events at hadron colliders are calculated, including finite-width effects and off resonance contributions for the entire decay chain, $t\to \mathrm{bW}\to \mathrm{bl}\nu ,$ for both top quarks. The resulting background rates to a Higgs boson search at the CERN large hadron collider are updated for inclusive $H\to \mathrm{WW}$ studies and for $H\to \tau \tau$ and $H\to \mathrm{WW}$ decays in weak boson fusion events. The finite-width effects are large, increasing $t\overline{t}\mathrm{}\left(j\right)\mathrm{}$ rates by 20% or more, after typical cuts which are employed for top-background rejection.