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Title Probing the standard model and nucleon sturcture via partiy violating electron scattering
Authors Thomas Humensky
JLAB number JLAB-PHY-03-251
LANL number (None)
Other number DOE/ER/40150-4579
Document Type(s) (Thesis) 
Supported by U.S. Naval Research: No
Supported by Jefferson Lab LDRD Funding: No
A PHD thesis
Advisor(s) :
   Gordon Cates (Princeton)
Publication Abstract: Parity-violating electron scattering has developed over the last 25 years into a tool to study both the structure of electroweak interactions and the structure of nucleons. This thesis reports work on two parity-violation experiments, the Hall A Proton Parity Experiment (HAPPEX) and SLAC E-158. HAPPEX (Jefferson Laboratory, 1998-1999) measured the parity-violating asymmetry in elastic e-p scattering at Q 2 = 0.477 GeV 2 . This asymmetry is sensitive to the proton's strange elastic form factors. An asymmetry of A LR = -15.05 ± 0.98(stat) ± 0.56(syst) ppm was measured. This asymmetry measurement allowed HAPPEX to set new constraints on the strange elastic form factors of the proton: [Special characters omitted.] where G Es and G Ms are the strange electric and magnetic form factors of the proton, respectively. The first error is the quadrature sum of the experimental errors and the second error is due to uncertainty in electromagnetic form factors. This result is consistent with the absence of a contribution from strange quarks. This thesis reports an analysis of the 1999 data set. SLAC E-158 is a measurement of the parity-violating asymmetry in Møller scattering. A 45-GeV longitudinally polarized electron beam is scattered off unpolarized electrons in a liquid hydrogen target at Q 2 = 0.025 GeV 2 . The asymmetry in this process is proportional to (1/4 - sin 2 [straight theta] W ), where [straight theta] W is the weak mixing angle. This measurement tests electroweak theory at the one-loop level and probes for new physics, including additional gauge bosons and electron compositeness. Within the Standard Model, the raw asymmetry is expected to be approximately 0.1 ppm. E-158 had engineering runs in 2000 and 2001 and its first physics runs in 2002. Data from the physics runs are currently being analyzed. One class of systematic error to which both of these experiments are sensitive is an asymmetry in the rate of scattered electrons due to helicity-correlated asymmetries in properties of the electron beam. This thesis describes work done in preparation for each experiment to understand and suppress those asymmetries. Results on beam asymmetries from the 1999 HAPPEX run and the 2000 E-158 engineering run are presented.
Experiment Numbers: E91-010
Group: Hall A
Document: pdf
Accepted Manuscript:
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