The W b anti-b, Z b anti-b and t anti-t b anti-b production at LHC are
irreducible backgrounds for possible observability of the Standard Model (SM)
and Minimal Supersymmetric Standard Model (MSSM) light Higgs boson respectively
in the associated WH, ZH and t anti-t H production followed by the H -> b
anti-b decay. We present a comparison of the background estimates as obtained
with (a) complete massive matrix element implemented in AcerMC Monte Carlo
generator and (b) PYTHIA implementation of the inclusive W, Z, and t anti-t
production, followed by the parton showering mechanism. Both approaches lead to
a production of the final state of interest, but differ in the approximations
used. We concentrate on the comparison of these approaches for the background
to the light Higgs boson searches at LHC.Comment: EPJC Referee's comments adde