Type of Document Dissertation Author Mammei, Juliette Mae URN etd-05112010-155435 Title Parity-Violating Elastic Electron Nucleon Scattering: Measurement of the Strange Quark Content of the Nucleon and Towards a Measurement of the Weak Charge of the Proton Degree PhD Department Physics Advisory Committee
Advisor Name Title Pitt, Mark L. Committee Chair Blecher, Marvin Committee Member Mizutani, Tetsuro Committee Member Schmittmann, Beate Committee Member Vogelaar, Robert Bruce Committee Member Keywords
- Strange quark
- transverse
- beam normal single spin asymmetry
- G0
- Qweak
Date of Defense 2010-04-30 Availability unrestricted Abstract The experiments discussed in this thesis exploit parity violation in elastic electron protonscattering in order to measure properties of the nucleon. Both experiments make use of
the high quality, highly polarized electron beam available at Thomas Jeff erson National
Accelerator Facility. Qweak will measure the weak mixing angle, sin2θW, via a measurement
of the weak charge of the proton, at a four-momentum transfer, Q2~0.026 GeV2/c2. The
precision of this measurement gives Qweak access to new physics at the scale of 2.3 TeV,
making it a test of the standard model. The G0 experimental program provides the fully
separated contributions of the strange quark to the charge and magnetization distributions of
the nucleon at two di fferent values of four-momentum transfer, Q2 ~ 0.22 and 0.63 GeV2/c2. The measurement of the strange quark content of the proton in the G0 experimental program
and other parity-violating electron scattering experiments provides a measurement of the
hadronic contribution to the asymmetry in Qweak.
In addition, G0 was able to measure the parity-conserving beam normal single spin
asymmetries that provide a measurement of the imaginary part of two photon exchange.
The measurement of this asymmetry is necessary to understand the systematic contribution
to measurements of parity-violating asymmetries, but it is also an important physics result.
Recent theoretical work has shown that higher order radiative eff ects, such as two photon
exchange, may be able to explain discrepancies between experiments which measure the ratio
of the electric and magnetic form factors of the proton. The measurement of the transverse or
beam normal single spin asymmetries provides a benchmark for theories that estimate the size
of radiative corrections that are important for precision electroweak scattering experiments
such as those described in this thesis. The results of the measurement of the transverse
asymmetries at backward angles in G0 are presented at the two values of Q2 ~ 0.22 and 0.63 GeV2/c2 for hydrogen. Results for deuterium, which can provide the first measurements of the beam normal single spin asymmetries on the neutron, are also presented.
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