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We present a search at the Jefferson Laboratory for new forces mediated by sub-GeV vector bosons with weak coupling ^' to electrons. Such a particle A^' can be produced in electron-nucleus fixed-target scattering and then decay to an e^+e^- pair, producing a narrow resonance in the QED trident spectrum. Using APEX test run data, we searched in the mass range 175--250 MeV, found no evidence for an A^'e^+e^- reaction, and set an upper limit of ^'/10^-6. Our findings demonstrate that fixed-target searches can explore a new, wide, and important range of masses and couplings for sub-GeV forces.
Abrahamyan et al. (Fri,) studied this question.