Re-evaluating Claims of Discovery in Data from the ATOMKI 5 MV Van De Graaf Accelerator

Using the electron-positron pair spectrometer at the 5 MV Van de Graaff-accelerator at the Institute for Nuclear Research, Hungarian Academy of Sciences (ATOMKI), Krasznahorkay et al. recently announced data not fitting the Standard Model of particle physics. They claim a 6.8 $\sigma$ excess in internal pair creation at high relative angles for the particle pair released in the isoscalar transition, indicative of a particle of mass circa 16.7 MeV. A hypothetical gauge boson, a carrier of a fifth force, has been proposed as an explanation for the excess. We show that a more mundane explanation may lie in the presence of additional nonresonant decay amplitudes, such as $\alpha$ decay of $^8$Be*. The short time scale for this decay, and the additional dynamics of the four-body system make $^8\text{Be*} \rightarrow 2\alpha e^+e^-$ decay a plausible candidate.