QCD corrections to tt̄bb̄ productions via photon-photon collisions at linear colliders

We calculated the complete next-to-leading order(NLO) QCD corrections to the tt̄bb̄ production process at a γγ collider in the standard model(SM). The calculation of the one-loop QCD correction includes the evaluations of the hexagon and pentagon amplitudes. We studied the NLO QCD corrected total cross section, the distributions of transverse momenta of final topand bottom-quark states, and the dependence of the cross section on renormalization scale μ. It shows that NLO QCD correction generally increases the LO cross section in our chosen parameter space, and the K-factor varies from 1.70 to 1.14 when colliding energy goes up from 400 GeV to 2 TeV . We find that the correction distinctly changes the distributions of transverse momenta of the final topand bottom-quark states, and the NLO QCD correction obviously improves the independence of the cross section for process γγ → tt̄bb̄ on the renormalization scale. PACS: 14.65.Ha, 14.80.Bn, 12.38.Bx