Probing Novel Properties of Nucleons and Nuclei via Parity Violating Electron Scattering

Thesis/Dissertation · Tue May 01 04:00:00 EDT 2012

DOI:https://doi.org/10.2172/1062690· OSTI ID:1062690

Mercado, Luis ^[1]

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1. Univ. of Massachusetts, Amherst, MA (United States)

This thesis reports on two experiments conducted by the HAPPEx (Hall A Proton Parity Experiment) collaboration at the Thomas Jefferson National Accelerator Facility. For both, the weak neutral current interaction (WNC, mediated by the Z⁰ boson) is used to probe novel properties of hadronic targets. The WNC interaction amplitude is extracted by measuring the parity-violating asymmetry in the elastic scattering of longitudinally polarized electrons o unpolarized target hadrons. HAPPEx-III, conducted in the Fall of 2009, used a liquid hydrogen target at a momentum transfer of Q² = 0.62 GeV². The measured asymmetry was used to set new constraints on the contribution of strange quark form factors (G^s_E,M ) to the nucleon electromagnetic form factors. A value of A_PV = -23.803±} 0.778 (stat)± 0.359 (syst) ppm resulted in G^s_E + 0.517G^s_M = 0.003± 0.010 (stat)± 0.004 (syst)± 0.009 (FF). PREx, conducted in the Spring of 2010, used a polarized electron beam on a 208Pb target at a momentum transfer of Q² = 0.009 GeV². This parity-violating asymmetry can be used to obtain a clean measurement of the root-mean-square radius of the neutrons in the ²⁰⁸Pb nucleus. The Z⁰ boson couples mainly to neutrons; the neutron weak charge is much larger than that of the proton. The value of this asymmetry is at the sub-ppm level and has a projected experimental fractional precision of 3%. We will describe the accelerator setup used to set controls on helicity-correlated beam asymmetries and the analysis methods for finding the raw asymmetry for HAPPEx-III. We will also discuss in some detail the preparations to meet the experimental challenges associated with measuring such a small asymmetry with the degree of precision required for PREx.

• Research Organization: Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 1062690
• Report Number(s): JLAB-PHY--12-1696; DOE/OR/23177--2483
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
73 NUCLEAR PHYSICS AND RADIATION PHYSICS