The Qweak experiment has precisely determined the weak charge of the proton Qp w by measuring the parity-violating asymmetry in elastic electron-proton scattering at a low momentum transfer of Q2 = 0.0249 (GeV/c)2 . Qpw has a definite prediction in the Standard Model, and a value of sin2 θW can be extracted from it for comparison with other neutral current observables. Qweak measured the weak charge of the proton to be Qpw(P V ES) = 0.0719 ± 0.0045, which is consistent with the Standard Model value of Qp w(SM) = 0.0708 ± 0.0003. Qweak ran at the Thomas Jefferson National Accelerator Facility for two and a half years and was installed in experimental Hall C. A 180µA beam of longitudinally polarized electrons at 1.16 GeV scattered off a liquid hydrogen target of unpolarized protons. The electrons were collimated to an acceptance of 5.8◦ to 11.6◦ and then passed through a magnetic spectrometer and onto quartz Čerenkov detector bars.
A detailed description of the theory and motivation behind the Qweak experiment is given. An overview of the Qweak apparatus and an in-depth discussion of the luminosity monitor performance is presented. A general overview of the Qweak analysis is also presented, with a focus on the beamline background correction, the nonlinearity measurement, and the simulation to constrain error for a rescattering effect. Also detailed here is the final, unblinded Qweak result, which determined Qpw to 6.2% and provided the highest precision measurement of sin2θW at low energy. / PHD / Q<sub>weak</sub> is a precision-frontier accelerator driven experiment that took place at Thomas Jefferson National Accelerator Facility. Precision-frontier exists alongside the better known energy-frontier (which includes well known labs like the Large Hadron Collider) and refers to experiments which precisely measure values which are predicted by the latest theory. Deviations in these measurements help rule out theories and are used by energy-frontier experiments to know where to look for new physics. The Q<sub>weak</sub> experiment measured the weak charge of the proton, which can be though of as the weak analog to electric charge. This value has never been measured before, and, since it is predicted to be small by current theory, is a good place to look for new physics. The value measured by this experiment indicates good agreement with the current theory. Even though there is good agreement with theory, Q<sub>weak</sub> is an important result which will help define future physics models.
In this thesis is an overview of the theoretical motivation of Q<sub>weak</sub>, a general overview of the experimental design, in-depth discussion of the background detectors, general overview of the analysis with detailed descriptions of the several important corrections.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/89476 |
| Date | 15 November 2017 |
| Creators | Duvall, Wade Sayer |
| Contributors | Physics, Pitt, Mark L., Huber, Patrick, Simonetti, John H., Piilonen, Leo E., Sharpe, Eric R. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/msword |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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