Searching for light feebly coupled particles beyond the Standard Model is an active experimental program motivated by the existence of dark matter, neutrino masses, and other outstanding problems in particle physics. Some of the most powerful searches for long-lived particles rely on visible decays, and are best carried out at high intensity beam dump facilities.
In this talk I will outline a new set of results that allow for the reliable prediction of long-lived particle production from a full electromagnetic cascade. This new "cascade production" channel leads to orders-of-magnitude increases in sensitivity for certain electron-coupling dominated models as compared to existing analyses.