Off resonance background effects in e+e−→tt¯H

The top quark Yukawa coupling to the intermediate mass Higgs boson can be determined in the reaction e+e−→tt¯H that, after taking into account decays, will be detected at the International Linear Collider through reactions with 8 particles in the final state. Such 2→8 reactions receive contributions from tens thousands of Feynman diagrams, already in the lowest order of Standard Model, most of which comprise background to resonant associated production and decay of the top quark pair and Higgs boson. We illustrate the background effects by comparing cross sections of three reactions, which represent different detection channels of e+e−→tt¯H, calculated with the complete sets of the lowest order Feynman diagrams with the corresponding signal cross sections calculated with the diagrams of associated production and decay of off mass shell top quark pair and Higgs boson only. The comparison that is performed with different selections of cuts shows that the background effects are sizeable, but they can be reduced by appropriate choice of cuts.