"$a \to e^+e^-$ (mixing with $\eta^\prime$)" of "Search for hadronic decays of feebly-interacting particles at NA62"

Number of expected $a \to e^+e^-$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\eta^\prime$ assuming production coupling $\theta_{\eta^\prime} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.