The X17 boson and the $^3$H$(p,e^+ e^-)^4$He and $^3$He$(n,e^+ e^-)^4$He processes: a theoretical analysis

TL;DR

This paper investigates electron-positron pair production in four-nucleon systems using advanced nuclear theory, exploring the potential impact of a hypothetical low-mass boson on the process and its experimental detectability.

Contribution

It provides a comprehensive theoretical analysis of pair production in four-nucleon systems, including the effects of a hypothetical boson within a chiral EFT framework and ab initio calculations.

Findings

Electromagnetic pair production is modeled with high-order chiral EFT.

Potential signatures of a low-mass boson could alter the pair production cross section.

Guidelines for future experiments to detect such effects are discussed.

Abstract

The present work deals with $e^+$-$e^-$ pair production in the four-nucleon system. We first analyze the process as a purely electromagnetic one in the context of a state-of-the-art approach to nuclear strong-interaction dynamics and nuclear electromagnetic currents, derived from chiral effective field theory ($\chi$EFT). Next, we examine how the exchange of a hypothetical low-mass boson would impact the cross section for such a process. We consider several possibilities, that this boson is either a scalar, pseudoscalar, vector, or axial particle. The ab initio calculations use exact hyperspherical-harmonics methods to describe the bound state and low-energy spectrum of the $A\,$=$\,4$ continuum, and fully account for initial state interaction effects in the $3+1$ clusters. While electromagnetic interactions are treated to high orders in the chiral expansion, the interactions of the hypothetical boson with nucleons are modeled in leading-order $\chi$EFT (albeit, in some instances, selected subleading contributions are also accounted for). We also provide an overview of possible future experiments probing pair production in the $A\,$=$\,4$ system at a number of candidate facilities.facilities.