The Measurement of a Lepton-Lepton Electroweak Reaction (MOLLER) Experiment*

The MOLLER experiment will measure the parity-violating asymmetry $A_{PV}$ in polarized electron-electron (M$\o$ller) scattering which arises due to the interference between the Standard Model electromagnetic and weak neutral current amplitudes. The experiment will run in Hall A of Jefferson Lab. The 11 GeV polarized electron beam with a current of 75 $\mu$A will be incident on a 1.5 m liquid hydrogen target. A two-toroid spectrometer system will focus scattered electrons (5 $< \theta_{lab} <$ 19 mrads) onto an array of 224 quartz Cherenkov detectors 28 m downstream of the target center. $A_{PV}$ at our kinematics ($Q^2$ = 0.0056 GeV$^2$) is predicted to be $\approx$ 35 parts per billion (ppb) and the statistical uncertainty of the measurement will be 0.7 ppb, resulting in a measurement of the weak charge of the electron of 2.4\% and a precision of $\pm$0.00024(stat)$\pm$0.00013(sys) of the weak mixing angle. This precision matches that of the single best determinations from high energy colliders, and is sensitive to physics beyond the Standard Model, such as multi-TeV-scale vector bosons, supersymmetry and light dark bosons among others. A summary of recent progress in the design of the apparatus and related R\&D efforts will be presented.