  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.
