New anomaly observed in He-4 supports the existence of the hypothetical X17 particle

Angular correlation spectra of e(+)e(-) pairs produced in the H-3(p, e(+)e(-)) He-4 nuclear reaction have been studied at E-p = 510, 610, and 900 keV proton energies. The main features of the spectra can be understood by taking into account the internal and external pair creations following the proton capture by H-3. However, these processes cannot account for an observed peak around 115 degrees in the angular correlation spectra. This anomalous excess of e(+)e(-) pairs can be described by the creation and subsequent decay of a light particle during the direct capture process. The derived mass of the particle is m(X)c(2) = 16.94 +/- 0.12(stat) +/- 0.21(syst) MeV. According to the mass this is likely the same X17 particle, which we recently suggested Whys. Rev. Lett. 116. 042501 (2016)] for describing the anomaly observed in the decay of Be-8.