The Q<sub>weak</sub> Experiment ran for two and a half years at the Thomas Jefferson National Accelerator Facility in pursuit of Q<sub>w</sub><sup>p</sup>, 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 (Q² = 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<sub>w</sub><sup>p</sup> (PVES) = 0.0719 ± 0.0045 was determined. The Standard Model has a definite prediction of Q<sub>w</sub><sup>p</sup> (SM) = 0.0708 ± 0.0003, consistent with the value determined by Q<sub>weak</sub> which sets a limit on possible new physics up to 7.5 TeV.
The theory behind the main measurement of the Q<sub>weak</sub> 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 Q<sub>weak</sub>'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 Q<sub>weak</sub> data. This data, combined with the inelastic data taken at nominal beam energy and a previous measurement, determined a constraint on d<sub>∆</sub> , a low energy constant related to hadronic parity violation, of (3.8 ± 14.7)g<sub>π</sub> . 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. / Doctor of Philosophy / The Q<sub>weak</sub> Experiment, run at the Thomas Jefferson National Accelerator Facility, measured the weak charge, the weak force analog of the electric charge of the electromagnetic force, of the proton. Unlike the well-know Large Hadron Collider, which operates on the energy-frontier and directly searches for new particles, Q<sub>weak</sub> operates by precisely measuring the results of scattering electrons off of protons. This approach is referred to as the precision frontier and is used to test the Standard Model, which has a well-defined prediction for the weak charge of the proton. Deviations from the Standard Model would suggest that there was new physics beyond the Standard Model affecting the results. However, the Q<sub>weak</sub> measured weak charge of the proton, Q<sub>w</sub><sup>p</sup> (PVES) = 0.0719 ± 0.0045, is in good agreement with the Standard Model predicted value. This provides a new limit, 7.5 TeV, on possible new physics beyond the Standard Model.
The theoretical background and apparatus of the Qweak experiment will be explained in this document. A vital component of the final result was understanding the path and energy of the electron as it passed through the apparatus. This was done via simulation but benchmarked by the tracking system. The tracking system will be explained in detail. The final analysis of the Q<sub>weak</sub> measurement of the weak charge will also be explained.
A secondary result discussed here focuses on data taken using the Q<sub>weak</sub> apparatus but at a different beam energy than the nominal Q<sub>weak</sub> data. For this data, the electron scatter inelastically off the proton. The lost kinetic energy of the electron causes the proton to be excited into the first resonance state, the ∆, which quickly decays away. This transition grants access to a low energy constant, d<sub>∆</sub>, and a measurement linked to the spins of the electrons being polarized perpendicular to the direction of the beam, B<sub>n</sub>. The extraction of these values is covered in detail.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/94345 |
| Date | 03 October 2019 |
| Creators | Lee, Anna R. |
| Contributors | Physics, Pitt, Mark L., Arav, Nahum, Huber, Patrick, Link, Jonathan M. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/x-zip-compressed |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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