We observed electron-positron pairs from the electro-magnetically forbidden M0 transition depopulating the 21.01 MeV 0− state in 4He. A peak was observed in their e+e− angular correlations at 115∘ with 7.2σ significance, and could be described by assuming the creation and subsequent decay of a light particle with mass of mXc2=16.84±0.16(stat)±0.20(syst) MeV and ΓX= 3.9×10−5 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 8Be.
@article{arxiv.1910.10459,
title = {New evidence supporting the existence of the hypothetic X17 particle},
author = {A. J. Krasznahorkay and M. Csatlos and L. Csige and J. Gulyas and M. Koszta and B. Szihalmi and J. Timar and D. S. Firak and A. Nagy and N. J. Sas and A. Krasznahorkay},
journal= {arXiv preprint arXiv:1910.10459},
year = {2019}
}