Determine the origin of the Atomki excesses

Determine the origin of the anomalous electron–positron excesses reported by the Atomki experiments, including whether they arise from a new 17 MeV boson or from backgrounds such as cosmic-ray muon coincidences and imperfect background subtraction.

Background

The paper simulates cosmic-ray muon backgrounds in the five-arm and six-arm electron–positron pair spectrometers used by the Atomki group. It finds that cosmic coincidences can generate energy and opening-angle structures resembling the reported anomalies, including enhancements near 140° in the 8Be transition window and near 120° in the 4He window.

Although these results demonstrate that cosmic-ray backgrounds may substantially affect the Atomki measurements, the simulations do not reproduce the actual beam-off data used by Atomki for background normalization and therefore do not establish whether the observed excesses are genuinely due to a new particle or are artifacts of cosmic-ray contamination and subtraction procedures.

References

While they do not settle the question of the origin of the Atomki excesses, these results highlight the critical importance of a robust cosmic-ray treatment in this type of measurements, and call for a detailed description of the beam-off studies supporting the search for anomalies in the $(, )$ distribution around the signal region.

— On the importance of cosmic-ray background in the Atomki anomaly  (2609.18383 - Benmansour et al., 16 Sep 2026) in Abstract