Search for a dark matter force mediator

We present an update of the A' Experiment (APEX) at the Thomas Jefferson National Accelerator Facility (JLab) in Virginia, USA. APEX searches for a new gauge boson ($A{^\prime}$) with sub-GeV mass and coupling to ordinary matter of $\alpha^\prime \sim (10^{-3} - 10^{-4})\alpha$, where $\alpha$ is the fine-structure constant. Electrons with an energy of 1--2 GeV impinge upon a fixed target of tungsten to produce an $A^\prime$ via a process analogous to photon bremsstrahlung, which then decays to an $e^+e^-$ pair that is detected by the JLab Hall A High Resolution Spectrometers. A test run was held in July of 2010, covering an $A^\prime$ mass range from 175 to 250 MeV and couplings $g^\prime/e > 10^{-3}$ . A full run is approved for 30 days of beam time and will cover $m_{A^\prime} \sim 65 - 250$~MeV. We will describe the experimental plan, which was recently re-optimized.