Search for long-lived particles with delayed photon signature in proton-proton collisions at \sqrt(s) = 13 TeV

We present a search for new physics involving long-lived particles decaying to delayed photons, using proton-proton collision data at √s = 13 TeV, collected by the CMS detector during 2016-2018, corresponding to 137 fb⁻¹ of integrated luminosity. The search focuses on delayed photon signatures, which arise from delayed decays of long-lived neutral particles, a key signature for probing physics beyond the Standard Model (SM). Results are interpreted in the context of Gauge-Mediated Supersymmetry Breaking (GMSB), where prompt gluino decays lead to a long-lived neutralino, which decays to a photon and a gravitino. To improve the identification of delayed photons, Deep Neural Networks (DNN) are employed for enhanced signal discrimination. Additionally, the ABCD method, a well-established data-driven approach, is used to estimate background contributions from SM processes. Furthermore, ECAL timing corrections were applied to ensure accurate measurement of photon arrival times, crucial for detecting delayed signals from long-lived particles. No significant deviation from SM expectations was observed, and upper limits on the production cross-section of long-lived particles are set, providing tighter constraints on the GMSB parameter space.