Cornering the X17 at PADME
E. Di Meco*,  On behalf of the PADME Collaboration, S. Bertelli, F. Bossi, D. Domenici, R. De Sangro, C. Di Giulio, G. Finocchiaro, L.G. Foggetta, M. Garattini, P. Gianotti, M. Mancini, I. Sarra, T. Spadaro, E. Spiriti, C. Taruggi, E. Vilucchi, V. Kozhuharov, K. Dimitrova, S.N. Ivanov, S. Ivanov, R. Simeonov, G. Georgiev, F. Ferrarotto, E. Leonardi, P. Valente, A. Variola, E. Long, G.C. Organtini, M. Raggi and A. Frankenthalet al. (click to show)
*: corresponding author
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Published on: December 05, 2025
Abstract
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.
DOI: https://doi.org/10.22323/1.489.0037
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