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$\sigma$ 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 $\Gamma_\mathrm{X}$= $3.9\times 10^{-5}$ 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.
- Publication:
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arXiv e-prints
- Pub Date:
- October 2019
- DOI:
- 10.48550/arXiv.1910.10459
- arXiv:
- arXiv:1910.10459
- Bibcode:
- 2019arXiv191010459K
- Keywords:
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- Nuclear Experiment
- E-Print:
- 5 pages, 4 figures