Cornering the X17 at PADME

The ATOMKI collaboration has recently confirmed the presence of the so-called "$^8$Be anomaly," now observed in the Internal Pair Creation (IPC) decay channels of $^4$He and $^{12}$C. This anomaly can be interpreted as the formation and subsequent decay of an intermediate particle with a mass of approximately 17 MeV, referred to as $X_{17}$. The primary objective of PADME Run III was to investigate the existence of $X_{17}$ and determine its nature, whether it is a vector or pseudo-scalar particle. The PADME experiment, at the INFN Laboratori Nazionali di Frascati, enables the production of \Xdicia via positron annihilation with electrons in a thin diamond fixed target. In 2020, during Run II, PADME collected data at a fixed center-of-mass energy of 20 MeV to search for evidence of a dark photon. In contrast, the recently concluded Run III operated at variable center-of-mass energies close to the expected mass of \Xdicia, aiming to detect an enhancement in the production of \ee pairs. By analyzing the data acquired through a fine energy scan around $\sqrt{s}=$ 17 MeV, any significant increase in cross-section, indicative of the production of a particle beyond Standard Model predictions, can be identified.