Search for new resonances decaying to pairs of merged diphotons in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A search is presented for an extended Higgs sector with two new particles, X and $\phi$, in the process X $\to$ $\phi \phi$ $\to$ $(\gamma \gamma )(\gamma \gamma )$. Novel neural networks classify events with diphotons that are merged and determine the diphoton masses. The search uses LHC proton-proton collision data at $\sqrt{s}$ = 13 TeV collected with the CMS detector, corresponding to an integrated luminosity of 138 fb${}^{-1}$. No evidence of such resonances is seen. Upper limits are set on the production cross section for $m_X$ between 300 and 3000 GeV and $m_{\phi }\mathrm{/}{m}_X$ between 0.5 and 2.5%, representing the most sensitive search in this channel.