Scientists working with the CMS detector at the Large Hadron Collider searched for signs of new physics in events that produce one high‑energy photon and a large amount of missing transverse momentum. Missing transverse momentum is a way to spot particles that do not interact with the detector, such as hypothetical dark matter or invisible gravitons from extra dimensions. The search used proton–proton collision data at a center‑of‑mass energy of 13 TeV collected in 2017–2018 (101 fb−1) and combined those data with earlier 2016 results to reach a total of 137 fb−1.

The team selected events that passed a single‑photon trigger (photon transverse momentum pT>200 GeV with about 95% trigger efficiency) and then required a missing transverse momentum above 200 GeV and one photon with transverse energy E_T>225 GeV in the central part of the electromagnetic calorimeter (the barrel, with |η|<1.44). The central region was chosen because it gives the cleanest and most precise photon measurements. Major backgrounds from known Standard Model processes include Z bosons decaying to neutrinos plus a photon, W bosons plus a photon, and photon production with jets. The analysis used control regions and simulation to estimate these backgrounds.

The results show no significant excess of events above the Standard Model expectation. The collaboration therefore set limits at the 95% confidence level on parameters in several theoretical scenarios. These include simplified dark matter models where a heavy mediator particle produces dark matter, an effective electroweak dark matter interaction that couples dark matter to photons and Z bosons, and the Arkani‑Hamed, Dimopoulos and Dvali (ADD) model of large extra spatial dimensions that predicts invisible graviton emission.