Explaining the ATOMKI X17 particle within the Standard Model

In 2016, Krasznahorkay $et$ $al.$ at the Institute for Nuclear Research, Hungarian Academy of Sciences (ATOMKI), announced data indicating the existence of a hypothetical gauge boson. In 2019 Krasznahorkay $et$ $al.$ announced additional evidence indicating the existence of the 'hypothetic X17 particle' in the form of $e^+e^-$ pairs from the M0 transition depopulating the 21.01 MeV $0^-$ state in $^4$He, with 7.2 $\sigma$ significance. We critically analyze the original results of ATOMKI as well as new evidence in the context of Standard Model processes, in particular interference effects between non-resonant decay amplitudes and higher-order QED corrections.