Still many things in our nature can not be explained by the Standard Model.
Many of these conundrums could be addressed by some of the best motivated models currently
under exploration, such as super-symmetry (SUSY), composite Higgs models and
extended Higgs models such as two-Higgs doublet models (2HDM). Most of these
extensions require additional scalar bosons. In particular, the 2HDM proposes
two new heavier neutral Higgs bosons, a scalar H and a pseudoscalar A.
ttbar is a very important (or say dominant) decaying channel of A/H,
especially for low tan\beta. Searches for A/H through the
gg->A/H->ttbar process are very challenging due to the peculiar behaviour of the
large interference effects with the SM ttbar background. Such
effects distort the signal shape from the normal peak-structure to be peak-dip
co-existing, which makes the signal generation and statistics treatment very
different from the traditional ways. The invariant mass of the ttbbar
candidate pair is reconstructed under the assumption of a semi-leptonic ttbar
decay. The final state is characterised by a single, high-pT electron or muon, large MET, and at least
four jets. The analysis will be presented, it is also the first A/H->ttbar searching result at LHC.
The results are further interpreted in the type-II 2HDM model, on the tan\beta
exclusion for several different A/H masses.