Evidence for and implications of a dark photon

Abstract: We performed the first global QCD analysis of electron-nucleon deep-inelastic scattering and related high-energy data by including the contribution from a dark photon. Our results revealed a significant reduction in $\chi^2$ relative to the baseline result without new physics. From a hypothesis test, our best dark photon fit is preferred over the Standard Model by as much as $6.5\ \sigma$, providing the first hint for the existence of a dark photon, although indirectly. Additionally, we explored the implications of a dark photon in party-violating electron scattering, rare kaon decay, and the electroweak precision observables. The dark photon as a portal connecting to dark matter particles was also discussed.