$H^0 \rightarrow Z^0 \gamma$ channel in ATLAS. \\ A study of the Standard Model and \\ Minimal Supersymmetric SM case

One of the potentially accessible decay modes of the Higgs boson in the mass region $100 < m_H < 180$ GeV is the $H^0 \rightarrow Z^0 \gamma$ channel. The work presented in this note examines the Standard Model and Minimal Supersymmetric Standard Model predictions for the observability of this channel using particle level simulation as well as the ATLAS fast simulation (ATLFAST). It compares present estimates for the signal observability with previously reported ones in \cite{unal} specifying the changes arising from the assumed energy of the colliding protons and the improvements in the treatment of theoretical predictions. With the present estimates, the expected significance for the SM Higgs does not exceed, in terms of $\frac{S}{\sqrt{B}}$, 1.5 $\sigma$ (including $Z^0 \rightarrow e^+ e^-$ and $Z^0 \rightarrow {\mu}^+ {\mu}^-$) for an integrated luminosity of $10^5$ pb$^{-1}$ therefore not favouring this channel for SM Higgs searches. Comparable discovery potential is expected at most for the MSSM $h^0 (H^0) \rightarrow Z^0 \gamma$ channel.