Detecting a Higgs Pseudoscalar with a $Z$ Boson at the LHC

We have adopted two Higgs doublet models to study the production of a Higgs pseudoscalar ($A^0$) in association with a $Z$ gauge boson from gluon fusion ($gg \to ZA^0$) at the CERN Large Hadron Collider. The prospects for the discovery of $ZA^0 \to \ell \bar{\ell} b\bar{b}$ are investigated with physics backgrounds and realistic cuts. Promising results are found for $m_A \alt 260$ GeV in two Higgs doublet models when the heavier Higgs scalar ($H^0$) can decay into a $Z$ boson and a Higgs pseudoscalar ($A^0$). Although the cross section of $gg \to ZA^0$ is usually small in the minimal supersymmetric standard model, it can be significantly enhanced in general two Higgs doublet models. This discovery channel might provide an opportunity to search for a Higgs scalar and a Higgs pseudoscalar simultaneously at the LHC and could lead to new physics beyond the Standard Model and the minimal supersymmetric model.