The Qweak Experiment: "A Search for New Physics at the TeV Scale via a Measurement of the Proton's Weak Charge"

After a decade of preparations, the Q(weak) experiment at Jefferson Lab is making the first direct measurement of the weak charge of the proton, Q p W. Because this quantity is suppressed in the Standard Model, a 4% result will significantly constrain new physics at the TeV scale while providing the most precise measurement of sin(2) theta(W) at low energies. Operationally, we measure the small (similar to -200 ppb) parity-violating asymmetry in electron-proton scattering in integrating mode while flipping the longitudinal polarization of the electrons up to 1000 times per second. Potential sources of new, parity-violating interactions between electrons and light quarks include a Z', lepto-quarks, and R-parity-violating SUSY. Our proton measurement provides isospin constraints which are nearly orthogonal to, and thus completely complementary to, older precise Cs APV data. Commissioning took place Fall 2010, and we completed Run I in May 2011 with 1/4 the statistics goal. After a 6 month shutdown, Run II began November 2011 and finished early summer 2012. The status of this enormous effort will be summarized.