Modelling of the tt+bb Process with the ATLAS Experiment

The measurement of the Yukawa coupling of the Higgs boson to the top quark is an important test of the Standard Model (SM). It could be used to either find deviations from the SM or to constrain BSM theories. To study this coupling, the production of a SM Higgs boson in association with a top-quark pair is used. The decay mode where the SM Higgs boson decays to bottom quarks has the highest branching ratio. Unfortunately, it suffers from a large tt+bb background. By reducing the modelling uncertainties of the tt+bb background, a better sensitivity for the signal process can be achieved. The state of the art theoretical description of the tt+bb background uses the four flavour scheme where the bottom quark is treated as a massive particle. To update the current set of Monte Carlo samples, newly generated samples are added. These MC samples differ in the choice of the renormalisation and factorisation scale, parton distribution function set and treatment of the bottom quark as a massive or a massless particle.