Probing the CP-violating light neutral Higgs in the charged Higgs decay at the LHC

The CP-violating MSSM allows existence of a light neutral Higgs boson ($M_{H_1} \lapp 50$ GeV) in the CPX scenario in the low $\tan \beta (\lapp 5)$ region, which could have escaped the LEP searches due to a strongly suppressed $H_1 Z Z$ coupling. This parameter space corresponds to a relatively light $H^\pm$ ($M_{H^\pm} < M_t$), which is predicted to decay dominantly into the $W H_1$ channel. Thus one expects to see a striking $t \bar t$ signal at the LHC, where one of the top quarks decays into the $bb \bar b W$ channel, via $t \to b H^\pm, H^\pm \to W H_1$ and $H_1 \to b \bar b$. The characteristic correlation between the $b \bar b$, $b \bar b W$ and $b b \bar b W$ invariant mass peaks is expected to make this signal practically free of the SM background. Our parton level Monte Carlo simulation yields upto 5000 events, for ${\cal L} = 30$ fb$^{-1}$, over the parameter space of interest, after taking into account the b-tagging efficiency for three or more b-tagged jets.