Search for the $U$ boson in the process $e^+ e^- \to U γ$, $U \to e^+ e^-$ with the KLOE detector

Abstract: Dark Matter and Dark Energy are two of the most fundamental open questions in physics today. The existence of a light dark-force mediator has been hypothesized as a possible explanation for several unexplained physical phenomena. A new search for this mediator, the dark photon $U$, is underway using data collected with the KLOE detector at DA$\Phi$NE. We describe the strategy we will use in our search for a resonant peak in the electron-positron invariant mass spectrum from the process $e^+e^- \to U \gamma$ with $U \to e^+e^-$. So far we found no evidence for the process and set a preliminary upper limit on the level of mixing between the secluded dark sector and the standard model.