Qweak: Measurement of the Proton's Weak Charge

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A search for physics beyond the Standard Model of fundamental interactions has been underway at Jefferson Laboratory in Newport News, VA, for over a decade. The Qweak experiment has already produced the world’s first measurement of the proton’s weak charge, a fundamental property that determines how a proton responds to the weak interaction. Over the next two years we will complete our meticulous analysis of over 180 Terabytes of data acquired during 2010-12 and be ready to publish the most precise measurement of a parity-violating asymmetry in electron-proton scattering, determining the proton’s weak charge to 5x higher precision, and setting new limits on the possible existence of new force-mediating subatomic particles beyond the Standard Model. The Canadian group has been a major player in this bold initiative since it was first proposed in 2001. With support from NSERC, CFI, TRIUMF, Jefferson Lab, and our home institutions, we designed, built, tested and took responsibility for the installation, commissioning and successful implementation of the Qweak magnetic spectrometer, the main detector array, the Compton polarimeter recoil electron detectors, the quartz scanner detector, and all of the low-noise current mode electronics and digital readout for the main detector and beamline / polarized source diagnostic devices. We led the evaluation of helicity-correlated systematic errors in the experiment and played a major role in their assessment during the commissioning and running phases of Qweak. We have trained numerous undergraduate, graduate, and postgraduate researchers during the course of this intensive campaign. Our present grant request will support the group’s ongoing efforts, including one research associate who is an expert in Monte Carlo simulations and particle tracking analysis, to complete the final stages of the data analysis and prepare results for publication.