arXiv:1910.10459nucl-ex
New evidence supporting the existence of the hypothetic X17 particle
Abstract
We observed electron-positron pairs from the electro-magnetically forbidden M0 transition depopulating the 21.01 MeV 0$^-$ state in $^4$He. A peak was observed in their $e^+e^-$ angular correlations at 115$^\circ$ with 7.2$σ$ significance, and could be described by assuming the creation and subsequent decay of a light particle with mass of $m_\mathrm{X}c^2$=16.84$\pm0.16 (stat) \pm 0.20 (syst)$ MeV and $Γ_\mathrm{X}$= $3.9\times 10^{-5}$ eV. According to the mass, it is likely the same X17 particle, which we recently suggested [Phys. Rev. Lett. 116, 052501 (2016)] for describing the anomaly observed in $^8$Be.
This result isn't even peer-reviewed yet. All of this hype about the X17 particle is coming from a pre-print on the arXiv. https://arxiv.org/abs/1910.10459 They claim a 7.2 sigma result, but the distribution of the null-hypothesis (called PDF(exp) in the paper) was determined…
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