The ttbb background to the Higgs searches: Pythia versus CompHEP rates.

The ttbb production is a dominant background for the SM and MSSM Higgs search in the associated production ttH with H->bb. This Note presents comparison for the background rates obtained with the Monte Carlo generators: PYTHIA5.7 and CompHEP. In the case of PYTHIA the tt production is generated in the hard process and the remaining two b-quarks are obtained from the partonic cascade. In the case of CompHEP exact matrix element for ttbb production is used. The detailed comparison of thecross-sections and expected acceptances are shown for several steps of the selection used for the extraction of the Higgs signal peak. Final estimates for the expected number of background events is similar in both cases with predictions from PYTHIA being even slightly higher. This comparison confirms good predictivity of the PYTHIA generator for the ttbb background channel.