X17 boson and the 2H(p, e plus e-) 3He and 2H(n, e plus e-) 3H processes: a theoretical analysis

The present work deals with the e+-e- pair production in the H2(p,e+e-)He3 and H2(n,e+e-)H3 processes, in order to make evident possible effects due to the exchange of a hypothetical low-mass boson, the so-called X17. These processes are studied for energies of the incident beams in the range 18-30 MeV, in order to have a sufficient energy to produce such a boson, whose mass is estimated to be around 17 MeV. We first analyze them as purely electromagnetic processes, 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 (χEFT). Next, we examine how the exchange of a hypothetical low-mass boson would impact the cross sections for such processes. We consider several possibilities: that this boson is either a scalar, pseudoscalar, vector, or axial particle. The main aim of the study is to exploit the specular structure of the He3 and H3 nuclei to investigate the isospin dependency of the X17-nucleon interaction, as the alleged "protophobicity."