Apex Experiment

APEX is one of several experiments hunting for the carrier of a new force, a hypothetical boson dubbed A’. This graph shows the range of the parameter space covered by these proposed experiments. The solid red is the slice of parameter space covered by APEX’s test run. The full APEX experiment will search the entire area above the red curve. See: PI Science: Hunting for New Forces

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We present a search at Jefferson Laboratory for new forces mediated by sub-GeV vector bosons with weak coupling $\alpha'$ 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 $A'\to e^+e^-$ reaction, and set an upper limit of $\alpha'/\alpha \simeq 10^{-6}$. Our findings demonstrate that fixed-target searches can explore a new, wide, and important range of masses and couplings for sub-GeV forces. See: Search for a new gauge boson in the $A'$ Experiment (APEX)

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Rouven Essig, Search for a New Vector Boson Decaying to e+e- (talk to Hall A Collaboration on APEX Motivation ).