Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)




Todd Averett


In the Standard Model, gauge bosons mediate the strong, weak, and electromagnetic forces. New forces could have escaped detection only if their mediators are either heavier than O (TeV) or weakly coupled to charged matter. New vector bosons with small coupling a' arise naturally from a small kinetic mixing with the photon and have received considerable attention as an explanation of various dark matter related anomalies. Such particles could be produced in electron-nucleus fixed-target scattering and then decay to e+ e -- pairs. New light vector bosons and their associated forces are a common feature of Standard Model extensions, but existing constraints are remarkably sparse. The APEX experiment will search for a new gauge boson A' with coupling alpha'/alphafs ≳ 6 x 10--8 to electrons in the mass range 65 MeV< mA'< 550 MeV. The experiment will study e + e-- production off an electron beam incident on a high-Z target in hall A at Jefferson Lab. The e-- and e+ will be detected in the High Resolution Spectrometers (HRSs). The invariant mass spectrum of the e+ e -- pairs will be scanned for a narrow resonance corresponding to the mass of the A'. A test run for the APEX experiment was held in the summer of 2010. Using the test run data, an A' search was performed in the mass range 175-250 MeV. The search found no evidence for an A' → e+ e-- reaction, and set an upper limit of alpha'/alpha fs ≳ 10--6.



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