Determination of the Proton's Weak Charge and Its Constraints on the Standard Model

This article discusses some of the history of parity-violation experiments that culminated in the Q(weak) experiment, which provided the first determination of the proton's weak charge Q(W)(P). The guiding principles necessary to the success of that experiment are outlined, followed by a brief description of the Q(weak) experiment. Several consistent methods used to determine Q(W)(p) from the asymmetry measured in the Q(weak) experiment are explained in detail. The weak mixing angle sin(2) theta(w) determined from Q(W)(p) is compared with results from other experiments. A description of the procedure for using the Q(W)(p) result on the proton to set TeV-scale limits for new parity-violating semileptonic physics beyond the Standard Model (BSM) is presented. By also considering atomic parity-violation results on cesium, the article shows how this result can be generalized to set limits on BSM physics, which couples to any combination of valence quark flavors. Finally, the discovery space available to future weak-charge measurements is explored.