Existence of a 17 MeV boson coupled to electrons
In plain words
If the X17 particle exists, it should also appear when positrons hit electrons at just the right energy. Dedicated experiments are scanning this energy.
Precise statement
Test for a vector or axial-vector boson with $m_X = 16.5 \text{ to } 17.2\,\mathrm{MeV}$ and electron coupling $\epsilon$ of roughly $2 \times 10^{-4} \text{ to } 1.4 \times 10^{-3}$ through resonant $e+ e- \to X \to e+ e-$ production (PADME), electron beam-dump and pair-spectrometer experiments. Answer: discovery, or exclusion at 90 percent confidence of the full coupling range implied by the ATOMKI 8Be and 4He rates.
What would settle it
A further PADME run at higher statistics and an independent resonant-production or beam-dump experiment covering the full coupling range.
Status in the literature
Unverified note: it names recent work and was partly written without a live literature search; it awaits a check by an editor.
PADME (arXiv 2505.24797, 2025) found an excess near 16.90 MeV with a global significance of about 2 standard deviations; no follow-up result had been published, to our knowledge, as of mid-2026.
Parent problems
- Special case of Origin of the ATOMKI 17 MeV pair-emission anomaly · open · from revision 1
Results
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