On the W+4 jets background to the top quark asymmetry at the Tevatron

We investigate the possibility that the W+4 jets background is a source of the anomalously large top-antitop (tt¯) charge asymmetry observed at the Tevatron. We simulate the tt¯ reconstruction of the signal and background events at the matrix-element level and find that the reconstructed tt¯ candidates from the W+4 jets background could give large forward-backward asymmetry. We suggest serious re-evaluation of the W+4 jets background for the tt¯ candidate events by studying the distributions of the reconstructed tt¯ systems in their rapidity difference, the transverse momentum of the top quark, and that of the tt¯ system, which can differ significantly from those of the QCD tt¯ production events especially at high tt¯ invariant mass.