Further Studies of Higgs Properties at An ILC γγ Collider

Recently the ATLAS and CMS experiments at the LHC have found a Higgs like boson $h$ with a mass around 125 GeV from several decay modes. The decay mode $h \to \gamma\gamma$ is one of the most important modes in studying whether $h$ is actually the standard model (SM) Higgs boson. Current data indicate that $h\to \gamma\gamma$ has a branching ratio larger than the SM prediction for $h$ being identified as the SM Higgs boson. To decide whether the $h$ discovered at the LHC is the SM Higgs boson, more data are needed. We study how $\gamma\gamma$ collider can help to provide some of the most important information about the Higgs boson properties. We show that a $\gamma\gamma$ collider can easily verify whether the enhanced $h \to \gamma\gamma$ observed at the LHC hold. Different models can be tested by studying Higgs boson decay to $\gamma Z$. Studying angular distribution of the $\gamma \gamma$ through on-shell production of $h$ and its subsequent decays into a $\gamma \gamma$ pair can decide whether the Higgs like boson $h$ at the LHC is a spin-0 or a spin-2 boson.