Ultralight bosons are promising dark matter candidates. This paper proposes a novel method to detect ultralight dark matter using dark mediators in collider and beam dump experiments. The time-varying nature of the dark mediator mass, modeled as a kinetic mixing dark photon, exhibits a double-peak spectrum, significantly reducing existing constraints. Using event time stamps from CMS Open Data, the sensitivity is further boosted by an order of magnitude, enabling detection of invisible decays of the dark mediator.
