Protophobic Fifth Force Interpretation of the Observed Anomaly in $^8$Be Nuclear Transitions

TL;DR

This paper proposes that a 17 MeV protophobic gauge boson explains an anomaly in $^8$Be nuclear transitions and could also address the muon g-2 discrepancy, introducing a new fifth force with specific couplings.

Contribution

It introduces a new protophobic gauge boson to explain nuclear transition anomalies and muon g-2 discrepancy, providing a unified theoretical framework.

Findings

A 17 MeV gauge boson explains the $^8$Be anomaly.

The boson mediates a fifth force with a 12 fm range.

Potential resolution of the muon g-2 discrepancy.

Abstract

Recently a 6.8$\sigma$ anomaly has been reported in the opening angle and invariant mass distributions of $e^+ e^-$ pairs produced in $^8\text{Be}$ nuclear transitions. The data are explained by a 17 MeV vector gauge boson $X$ that is produced in the decay of an excited state to the ground state, $^8\text{Be}^* \to {}^8\text{Be} \, X$, and then decays through $X \to e^+ e^-$. The $X$ boson mediates a fifth force with a characteristic range of 12 fm and has milli-charged couplings to up and down quarks and electrons, and a proton coupling that is suppressed relative to neutrons. The protophobic $X$ boson may also alleviate the current 3.6$\sigma$ discrepancy between the predicted and measured values of the muon's anomalous magnetic moment.