Precision measurement of the weak charge of the proton and parity violation in the N → Δ transition

Thesis/Dissertation · Fri Sep 13 00:00:00 EDT 2019

DOI:https://doi.org/10.2172/1574105· OSTI ID:1574105

Lee, Anna ^[1]

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1. Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States)

The Q_weak 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. Q_weak 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$$^p_w$$ (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 Q_weak which sets a limit on possible new physics up to 7.5 TeV. The theory behind the main measurement of the Q_weak 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 Q_weak'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_weak's final result is outlined, as are additional physics results related to the N → Δ transition. During April 2012, an opportunity was seized to take ancillary data on the inelastic N → Δ transition at a different beam energy(877 MeV) than the nominal Q_weak data. This data, combined with the inelastic data taken at nominal beam energy and a previous measurement, determined a constraint on d_Δ, 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 → Δ transition of 149 ± 3 (stat) ± 72 (syst) ppm. This document includes both the longitudinal and transverse analysis of the 877 MeV data.

• Research Organization: Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 1574105
• Report Number(s): JLAB-PHY-19-3083; DOE/OR/23177-4812
• Country of Publication: United States
• Language: English