Implications of last NA64 results and the electron $g_{e}-2$ anomaly for the X(16.7) boson survival

Abstract

We point out that last NA64 bound on coupling constant of hypothetical $X(16.7 MeV)$ vector boson with electrons plus the recent value of the anomalous electron magnetic moment exclude at 90 \% C.L. purely vector or axial vector couplings of $X(16.7)$ boson with electrons. Models with nonzero $V \pm A$ coupling constant with electron survive and they can explain both the electron and muon $g - 2$ anomalies.