A Standard Model Explanation for the "ATOMKI Anomaly"
Abstract
Using the $e^+e^-$ pair spectrometer at the 5 MV Van de Graaff accelerator at the Institute for Nuclear Research, Hungarian Academy of Sciences (ATOMKI), Krasznahorkay et al. have claimed a 6.8$\sigma$ excess at high $e^+e^-$ opening angles in the internal pair creation isoscalar transition $^8\mathrm{Be}(18.15)\to\,^8\mathrm{Be}\,e^+e^-$. A hypothetical gauge boson with the mass circa $17$ MeV, "X17", has been proposed as an explanation for the excess. We show that the observed experimental structure can be reproduced within the Standard Model by adding the full set of second-order corrections and the interference terms to the Born-level decay amplitudes considered by Krasznahorkay et al. We implement a detailed model of the ATOMKI detector, and also show how experimental selection and acceptance bias exacerbate the apparent difference between the experimental data and the Born-level prediction.
- Publication:
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arXiv e-prints
- Pub Date:
- February 2021
- DOI:
- 10.48550/arXiv.2102.01127
- arXiv:
- arXiv:2102.01127
- Bibcode:
- 2021arXiv210201127A
- Keywords:
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- High Energy Physics - Phenomenology;
- Nuclear Experiment;
- Nuclear Theory
- E-Print:
- 7 pages, 10 figures. v2 corrects small typos and replaces images with vector graphics