APEX: A Prime EXperiment at Jefferson Lab

APEX is an experiment at Thomas Jefferson National Accelerator Facility (JLab) in Virginia, USA, that searches for a new gauge boson ($A^{\mathrm{\prime }}$) with sub-GeV mass and coupling to ordinary matter of $g^\prime \sim (10^{-6} - 10^{-2}) e$\mathrm{.}Electronsimpingeuponafixedtargetofhigh-Zmaterial\mathrm{.}An$A^\prime$ is produced via a process analogous to photon bremsstrahlung, decaying to an $e^{+}{e}^{-}$ pair. A test run was held in July of 2010, covering $m_{A^{\mathrm{\prime }}}$ = 175 to 250 MeV and couplings $g^\prime/e ; \textgreater ; 10^{-3}$\mathrm{.}Afullrunisapprovedandwillcover$m_{A^\prime} \sim$ 65 to 525 MeV and $g^{\mathrm{\prime }}\mathrm{/}e\text{textgreater}2.3\times {10}^{-4}$.