  The top quark Yukawa coupling to the intermediate mass Higgs boson can be
determined in the reaction e+e- -> t anti-t 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- -> t anti-t 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.
