title: Protophobic Fifth-Force Interpretation of the Observed Anomaly in ^{8}Be Nuclear Transitions.
abstract: Recently a 6.8σ anomaly has been reported in the opening angle and invariant mass distributions of e^{+}e^{-} pairs produced in ^{8}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}Be^{*}→^{8}Be X, and then decays through X→e^{+}e^{-}. The X boson mediates a fifth force with a characteristic range of 12 fm and has millicharged 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 3.6σ discrepancy between the predicted and measured values of the muon's anomalous magnetic moment.
authors: Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA.
authors: Jonathan L
authors: JL
authors: Feng
authors: Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA.
authors: Bartosz
authors: B
authors: Fornal
authors: Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA.
authors: Iftah
authors: I
authors: Galon
authors: Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA.|Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506-0055, USA.
authors: Susan
authors: S
authors: Gardner
authors: Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA.
authors: Jordan
authors: J
authors: Smolinsky
authors: Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA.
authors: Tim M P
authors: TM
authors: Tait
authors: Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA.
authors: Philip
authors: P
authors: Tanedo