Status of the JLab Eta Factory (JEF) experiment*

The JLab Eta Factory (JEF) experiment is an approved experiment in Hall D at Jefferson Lab that focuses on decays of $\eta$ mesons produced in the reaction $\gamma p \to p \eta$ with emphasis on the rare $\eta\to\pi^0\gamma\gamma$ channel. In addition to providing a rare window into higher-order chiral perturbation theory, this channel can be used to search for evidence of dark matter. A potential extension to the Standard Model posits a dark gauge boson $B$ that couples predominately with quarks and can be observed in the $\eta\to\gamma B$, $B\to\pi^0\gamma$ channel\footnote{S.~Tulin, Phys.\ Rev.\ D {\bf 89}, no. 11, 114008 (2014).}. The same set of final state particles can also be used to look for a scalar dark matter mediator $S$ in the $\eta\to\pi^0S$, $S\to\gamma\gamma$ channel\footnote{B.~Batell, A.~Freitas, A.~Ismail and D.~McKeen, arXiv:1812.05103 [hep-ph].}. In order to achieve the requisite resolution to clearly identify these rare channels, this experiment calls for an upgrade to the existing GlueX equipment, which is a fixed target apparatus based on a 2-Tesla solenoid magnet (which enables reconstruction of the momentum of the recoil proton). Neutral particles emerging after the interaction of the photon beam with a liquid hydrogen target are detected in the forward direction in the Forward Calorimeter (FCAL), an array of lead glass blocks. We plan to replace the $\sim$80$\times$80 cm$^2$ region of the FCAL closest to the beam line with an array of 2$\times$2$\times$20 cm$^3$ lead tungstate crystals. The current status of the JEF project will be presented.