Potential for the discovery of the protophobic boson at the STCF

Abstract: We study the morphology of the main drift chamber (MDC) proposed to be built around the collision point at the upcoming Super tau-charm facility (STCF), to check for its suitability in discovering the 17 MeV protophobic boson (X17 boson), hypothesised as a solution to the persistent ATOMKI nuclear-transition anomalies. These anomalies, observed in the excited $^8$Be, $^4$He, $^{12}$C, $^{16}$O nuclear transitions, have been interpreted as evidence for a $\sim$17 MeV, protophobic vector boson. Using the TrackEff framework, we perform detector-level simulations of the STCF MDC, and evaluate displaced-vertex sensitivities towards the protophobic boson, across the relevant mass-coupling parameter space. We study benchmark scenarios with visible and dark decay channels to perform likelihood-based significance estimates in order to determine the 5$σ$ discovery reach for the protophobic boson. We find that STCF can discover the protophobic boson while tolerating $\sim 10^4$ background events for specific regions of the parameter space around the 17 MeV peak. Our analysis establishes the first feasibility study of displaced light-boson searches at the STCF, motivating a full Geant-4 simulation.