Realistic model for a fifth force explaining anomaly in ${}^{8}B{e}^{\ast }\to {}^{8}Be{e}^{+}{e}^{-}$ Decay

Abstract

A $6.8\ddot{I}ƒ$ anomaly has been reported in the opening angle and invariant mass distributions of $e^{+}{e}^{-}$ pairs produced in ${}^{8}Be$ nuclear transitions. It has been shown that a protophobic fifth force mediated by a $17\text{MeV}$ gauge boson $X$ with pure vector current interactions can explain the data through the decay of an excited state to the ground state, ${}^{8}B{e}^{\ast }\to {}^{8}BeX$, and then the followed saturating decay $X\to e^{+}{e}^{-}$. In this work we propose a renormalizable model to realize this fifth force. Although axial-vector current interactions also exist in our model, their contributions cancel out in the iso-scalar interaction for ${}^{8}B{e}^{\ast }\to {}^{8}BeX$. Within the allowed parameter space, this model can alleviate the $(g-2{)}_{\hat{I}}¼$ anomaly problem and can be probed by the LHCb experiment. Several other implications are discussed.

RevTex, 9 pages with no figures. New major changes are made to the older version