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arXiv · 2504.11439

Combined Evidence for the $X_{17}$ Boson After PADME Results on Resonant Production in Positron Annihilation

Fernando Arias-Aragón·Giovanni Grilli di Cortona·Enrico Nardi·Claudio Toni
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Abstract

The Positron Annihilation into Dark Matter Experiment at the Laboratori Nazionali di Frascati has reported an excess of $e^+e^-$ final-state events from positron annihilation on fixed-target atomic electrons. While the global significance remains at the $(1.77\pm 0.15)\,\sigma$ level, the excess is centered around $\sqrt{s} \sim 17\,\text{MeV}$, coinciding with the invariant mass at which anomalous $e^+e^-$ pair production has previously been observed in nuclear transitions from excited to ground states in $^8$Be, $^4$He and $^{12}$C, thereby strengthening the case for a common underlying origin, possibly involving a hypothetical new $X_{17}$ boson. We discuss the significance of this independent accelerator-based evidence. Combining it with existing nuclear physics results, we obtain a value for the $X_{17}$ mass of $m_{X_{17}} = 16.88 \pm 0.05\,\text{MeV}$, reducing the uncertainty from nuclear physics determinations by more than a factor of two, and mitigating the impact of poorly known correlations among their systematic errors.

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Fernando Arias-Aragón, Giovanni Grilli di Cortona, Enrico Nardi, Claudio Toni. 2025-04-15. Combined Evidence for the $X_{17}$ Boson After PADME Results on Resonant Production in Positron Annihilation. https://doi.org/10.1140/epjc%2Fs10052-026-15587-2

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