An updated view on the ATOMKI nuclear anomalies

Abstract

In view of the latest experimental results recently released by the ATOMKI collaboration, we critically re-examine the possible theoretical interpretation of the observed anomalies in terms of a new BSM boson $X$ with mass $\sim 17$MeV. To this end we employ a multipole expansion method and give an estimate for the range of values of the nucleon couplings to the new light state in order to match the experimental observations. Our conclusions identify the axial vector state as the most promising candidate, while other spin/parity assignments seems disfavored for a combined explanation. This results is however based on an order of magnitude estimate for the, currently unknown, axial nuclear matrix element of the ${}^{12}$C transition, that needs then to be evaluated before being able to draw a definite conclusion. Intriguingly, an axial vector state can also simultaneously accommodate other experimental anomalies, {\emph{i.e.}} the KTeV anomaly in ${\pi }^0\to e^{+}{e}^{-}$ decay while being compatible with the conflicting measurements of the anomalous magnetic moment of the electron $(g-2{)}_e$ and other constraints on the electron couplings of the $X$ boson. The PADME experiment will completely cover the relevant region of the parameter space, thus allowing for a strong test of the existence of the $X$ particle.

arXiv comment42 pages, 9 figures, matches published version and erratum (results unchanged)

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Cited by in corpus (10)

• QED Meson Description of the X17 and Other Anomalous Particles
• Neutrino Constraints and the ATOMKI X17 Anomaly
• Ab initio investigation of the ${}^7$Li($p,e^{+}{e}^{-}$)${}^8$Be process and the X17 boson
• On the question of quark confinement in the Abelian U(1) QED gauge interaction
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• Dark hyperCharge Symmetry
• The X17 with Chiral Couplings
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