Motivated by the diphoton resonance recently reported by the ATLAS and CMS collaborations at $\sqrt{s}=13\mathrm{TeV}$, we interpret the resonance as a scalar boson $X(750)$ in hidden-valley-like models. The scalar boson $X$ can mix with the standard model Higgs boson and thus can be produced via gluon fusion. It then decays into a pair of very light hidden particles $Y$ of $\mathcal{O}(1\mathrm{GeV})$, each of which in turn decays to a pair of collimated ${\pi }^0$’s, and these two ${\pi }^0$’s decay into photons which then form photon jets. A photon jet ($\gamma$ jet) is a special feature that consists of a cluster of collinear photons from the decay of a fast moving light particle [$\mathcal{O}(1\mathrm{GeV})$]. Because these photons inside the photon jet are so collimated that it cannot be distinguished from a single photon, in the final state of the decay of $X(750)$ a pair of photon jets looks like a pair of single photons, which the experimentalists observed and reconstructed the 750 GeV diphoton resonance. Prospects for LHC Run-2 about other new and testable features are also discussed.

• Received 6 January 2016

DOI:https://doi.org/10.1103/PhysRevD.93.075013