# Can nuclear physics explain the anomaly observed in the internal pair production in the Beryllium-8 nucleus?

## TL;DR

This paper investigates whether refined nuclear physics models, including anisotropy and interference effects, can explain the Beryllium-8 pair production anomaly without invoking new particles.

## Contribution

It introduces an improved nuclear physics modeling approach using effective field theory to analyze the Beryllium-8 anomaly, emphasizing the role of transition form factors and interference effects.

## Key findings

- Refined modeling reduces the anomaly's significance.
- Interference effects influence pair emission anisotropy.
- Transition form factors may account for the observed excess.

## Abstract

Recently the experimentalists in [PRL 116, 042501 (2016)] announced observing an unexpected enhancement of the electron-positron pair production signal in one of the Beryllium-8 nuclear transitions. The following studies have been focused on possible explanations based on introducing new types of particle. In this work, we improve the nuclear physics modeling of the reaction by studying the pair emission anisotropy and the interferences between different multipoles in an effective field theory inspired framework, and examine their possible relevance to the anomaly. The connection between the previously measured on-shell photon production and the pair production in the same nuclear transitions is established. These improvements, absent in the original experimental analysis, should be included in extracting new particle's properties from the experiment of this type. We then study the possibility of using the nuclear transition form factor to explain the anomaly. The reduction of the anomaly's significance by simply rescaling our predicted event count is also investigated.