Many interesting questions have been brought into focus with the observations of three perplexing objects: (i) a neutral X17 boson with a mass of about 17 MeV at Atomki, (ii) a neutral E38 boson with a mass of about 38 MeV at Dubna, and (iii) the soft photon anomaly of excess (e+ e-) pairs with a transverse momentum of a few MeV/c to many tens of MeV/c at CERN. These three extra-ordinary candidate objects appear to lie outside the domain of the Standard Model. Many speculative ideas have been proposed for these objects, including the fifth force of Nature, the extension of the Standard Model, the QCD axion, cold quark-gluon plasma, and dark matter. In a recent publication, Cheuk-Yin Wong of the Physics Division at Oak Ridge National Laboratory is able to offer a coherent Standard Model description of these objects and suggests further research to study their properties and implications.
In connection with the soft photon anomaly that was consistently observed in experiments over many decades, it was previously noted that owing to its simultaneous and correlated production alongside with hadrons, a parent particle of the anomalous soft photons of excess (e+ e-) pairs is likely to contain elements of the hadron sector, such as a light quark and a light antiquark. The parent particle cannot arise from a quark-antiquark pair interacting with the quantum chromodynamical (QCD) interaction, because the QCD interaction will endow the pair with a mass much greater than the anomalous soft photon mass. It was therefore proposed that a quark and an antiquark interacting with the quantum electrodynamical (QED) interaction may give rise to new open string bound states (QED-meson states) with a mass of many tens of MeV. These QED mesons may be produced simultaneously with the QCD mesons in the string fragmentation process in high-energy collisions, and the excess (e+e-) pairs in the soft photon anomaly may arise from the decays of these QED mesons. The predicted masses of the neutral isoscalar and isovector QED mesons are close to the masses of the hypothetical X17 and E38 particles observed recently, making them good candidates for these particles [1].
If the QED meson description to these perplexing objects is confirmed by future experimental and theoretical works, it would open up the possibility that QED mesons and particles of similar types may be produced in the early evolution of the Universe after the big bang, during the quark-gluon plasma phase transition stage. They may provide non-baryonic massive material for subsequent astrophysical evolution and may be a source of non-baryonic black-holes, (e+ e-) emitters, and gamma ray emitters. Confirmation and further examination of the X17 and E38 particles, which are within the realm of standard nuclear physics, are therefore of great interest.
[1] C. Y. Wong, Journal of High Energy Physics, In Press
