Atomic Physics Constraints on the X Boson

TL;DR

This paper investigates the potential effects of a hypothesized 16.7 MeV X boson, suggested by recent experimental anomalies, on atomic systems, especially muonic atoms, to aid in its detection and characterization.

Contribution

It analyzes the impact of the X boson on electronic and muonic atoms, identifying muonic atoms with low to intermediate nuclear charge as promising systems for detection.

Findings

Muonic atoms of low and intermediate nuclear charge are most sensitive to the X boson.

The X boson effects can be distinguished from nuclear-size effects in these atomic systems.

Atomic physics experiments can provide constraints on the properties of the X boson.

Abstract

Recently, a peak in the light fermion pair spectrum at invariant q^2 approximately equal to 16.7 Me^2. has been observed in the bombardment of Li-7 by protons. This peak has been interpreted in terms of a protophobic interaction of fermions with a gauge boson (X boson) of invariant mass of approximately 16.7 MeV which couples mainly to neutrons. High-precision atomic physics experiments aimed at observing the protophobic interaction need to separate the X boson effect from the nuclear-size effect, which is a problem because of the short range of the interaction 11.8 fm, which is commensurate with a "nuclear halo". Here, we analyze the X boson in terms of its consequences for both electronic atoms as well as muonic hydrogen and deuterium. We find that the most promising atomic systems where the X boson has an appreciable effect, distinguishable from a finite-nuclear-size effect, are muonic atoms of low and intermediate nuclear charge numbers.