Search for exotic Higgs boson decays H to AA to 4 photons with events containing two merged photons in proton-proton collisions at sqrt(s) = 13 TeV

The result of a direct search for the exotic Higgs boson decay $\mathrm{H}\rightarrow\mathcal{A}\mathcal{A}$, $\mathcal{A}\rightarrow\gamma\gamma$ is presented, using events with a final state containing two photons. The hypothetical particle $\mathcal{A}$ is a low-mass, boosted scalar decaying promptly to two highly merged photons, misreconstructed as a single photon-like object. The data were collected by the CMS experiment at the CERN LHC from proton-proton collisions at $\sqrt{s} = 13~\mathrm{TeV}$, corresponding to an integrated luminosity of $136~\mathrm{fb}^{-1}$. No excess of events above the estimated background is found. Upper limits on the branching fraction $\mathcal{B}(\mathrm{H} \rightarrow \mathcal{A}\mathcal{A} \rightarrow 4\gamma)$ of 0.9--3.3 $\times10^{-3}$ are set at the $95\%$ confidence level for masses of $\mathcal{A}$ in the range $0.1 < m_{\mathcal{A}} < 1.2~\mathrm{GeV}$.