Precision measurement of the weak charge of the proton and parity violation in the N → ∆ transition
Lee, Anna R.
MetadataShow full item record
The Qweak Experiment ran for two and a half years at the Thomas Jefferson National Accelerator Facility in pursuit of Q^p_w , the neutral weak analog to the electric charge of the proton. Qweak measured the parity-violating asymmetry in elastic electron-proton scattering at an extreme forward angle (Q^2 = 0.0249 (GeV/c)^2 ). From the data gathered via the 1.16 GeV 180 μA longitudinally polarized electron beam scattering off the unpolarized photons in the liquid hydrogen target, a value of Q^p_w (PVES) = 0.0719 ± 0.0045 was determined. The Standard Model has a definite prediction of Q^p_w (SM) = 0.0708 ± 0.0003, consistent with the value determined by Qweak which sets a limit on possible new physics up to 7.5 TeV. The theory behind the main measurement of the Qweak Experiment is described in this document, along with the apparatus that made the measurement possible. Understanding the kinematics of the apparatus was a vital component to Qweak 's final measurement. An in-depth explanation of the tracking system responsible for benchmarking the momentum transfer and scattering angle simulations is included. The unblinded analysis of Qweak's final result is outlined, as are additional physics results related to the N→ ∆ transition. During April 2012, an opportunity was seized to take ancillary data on the inelastic N→ ∆ transition at a different beam energy(877 MeV) than the nominal Qweak data. This data, combined with the inelastic data taken at nominal beam energy and a previous measurement, determined a constraint on d_∆ , a low energy constant related to hadronic parity violation, of (3.8 ± 14.7)g_π . It also resulted in a measurement of the beam-normal single-spin asymmetry of the N→ ∆ transition of 149 ± 3 (stat) ± 72 (syst) ppm. This document includes both the longitudinal and transverse analysis of the 877 MeV data.
- Doctoral Dissertations