Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)




John Michael Finn

Committee Member

David S Armstrong


The differential cross section for elastic scattering of longitudinally-polarized electrons from protons exhibits a parity-violating asymmetry, due to the interference between weak and electromagnetic amplitudes. The asymmetry is extracted from the detector counting rates as APV = ( Dr - Dl)/(Dr + D l) where Drl are related to the right (left) differential cross sections sigmar, sigmal respectively. Thus APV = (sigmar - sigma l)/(sigmar + sigmal) for right-handed and left-handed electrons. This asymmetry is sensitive to the presence of strange sea quarks in the proton, in particular to the strange vector matrix elements GsE and GsM .;In an experiment performed in April--May 1998 and May 1999 in Hall A at the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab, data were obtained for a total of 179.6 Coulombs of incident electrons. Elastically-scattered electrons corresponding to an average Q 2 = 0.477(GeV/c)2 were detected in a pair of high-resolution spectrometers.;The excellent stability of the CEBAF beam led to negligible contribution from false asymmetries; Averaged over the experiment, the helicity-correlated beam position differences were less than 10nm and the helicity-correlated beam intensity asymmetries were less than 1 ppm.;The result APV = -15.05 +/- 0.98(stat) +/- 0.56(syst) ppm was measured at the kinematic point 〈thetalab〉 = 12.3?? and 〈 Q2〉 = 0.447 (GeV/c)2. Comparing the experimental asymmetry with the theoretical asymmetry, A th, allows extraction for the value of the strange form factor &parl0;GsE+ 0.392GsM&parr0;/&parl0;Gp M/mp&parr0; = 0.069 +/- 0.056 +/- 0.039, where the first error is experimental and the second arises from uncertainty in the electromagnetic form factors.



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