Early Results from the Qweak Experiment

A subset of results from the recently completed Jefferson Lab Q(weak) experiment are reported. This experiment, sensitive to physics beyond the Standard Model, exploits the small parity-violating asymmetry in elastic ep scattering to provide the first determination of the proton's weak charge Q(w)(p). The experiment employed a 180 mu A longitudinally polarized 1.16 GeV electron beam on a 35 cm long liquid hydrogen target. Scattered electrons in the angular range 6 degrees < theta < 12 degrees corresponding to Q(2) = 0.025 GeV2 were detected in eight Cerenkov detectors arrayed symmetrically around the beam axis. The goals of the experiment were to provide a measure of Q(w)(p) to 4.2% (combined statistical and systematic error), which implies a measure of sin(2)(theta(w)) at the level of 0.3%, and to help constrain the vector weak quark charges C-1u and C-1d. The experimental method is described, with particular focus on the challenges associated with the world's highest power LH2 target. The new constraints on C-1u and C-1d provided by the subset of the experiment's data analyzed to date will also be shown, together with the extracted weak charge of the neutron.