New anomaly observed in 4He 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.

Automated summary

Angular correlation spectra of e(+)e(-) pairs produced in the H-3(p, e(+)e(-)) He-4 nuclear reaction have been studied, revealing an anomalous excess of pairs possibly explained by the creation and subsequent decay of a light particle during the direct capture process. The derived mass of the particle suggests it may be the previously suggested X17 particle for explaining anomalies observed in the decay of Be-8.