  In this paper, the top quark pair production events are analyzed as a source
of neutral Higgs bosons of two Higgs doublet model type I at LHC. The
production mechanism is $pp \to H/A \to t\bar{t}$ assuming a fully hadronic
final state through $t \to Wb \to jjb$. In order to distinguish the signal from
the main background which is the standard model $t\bar{t}$, we benefit from the
fact that the top quarks in signal events acquire a large Lorentz boost due to
the heavy neutral Higgs boson. This feature leads to three collinear jets (a
fat jet) which is a discriminating tool for identification of the top quarks
from the Higgs boson resonances. Events with two identified top jets are
selected and the invariant mass of the top pair is calculated for both signal
and background. It is shown that the low $\tan\beta$ region has still some
parts which can be covered by this analysis and has not been excluded yet by
flavor physics data.
