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Title Measurement of Polarization Observables in the Electro-Excitation of the Proton to its First Excited State
Authors Rikki Roche
JLAB number JLAB-PHY-03-157
LANL number (None)
Other number DOE/ER/40150-2744
Document Type(s) (Thesis) 
Supported by U.S. Naval Research: No
Supported by Jefferson Lab LDRD Funding: No
A PHD thesis
Advisor(s) :
   Adam J. Sarty (Florida State University)
Publication Abstract: This thesis reports results from the Thomas Jefferson National Accelerator Facility (Jefferson Lab) Hall A experiment E91-011, which measured double-polarization observables in the pion electroproduction reaction from the proton. Specifically, the experiment measured the recoil proton polarization, polarized response functions, and cross section for the \( p\left( \overrightarrow{e},e^{\prime }\overrightarrow{p}\right) \pi ^{\circ } \) reaction at a center-of-mass energy centered at \( W \) = 1232 MeV - the peak of the \( \Delta \)(1232) resonance - and at a four-momentum transfer squared of \( Q^{2} \) = 1.0 GeV\( ^{2} \)/\( c^{2} \). Both the recoil proton polarization and polarized response function results will be presented in this thesis. Data were collected at Jefferson Lab, located in Newport News, Virginia during the summer of 2000. A 4.53 GeV polarized electron beam was scattered off of a cryogenic hydrogen target. The recoil proton polarization was measured in the Focal Plane Polarimeter (FPP), located in one of the two High Resolution Spectrometers (HRS) in Hall A. A maximum likelihood method was used to determine the polarized response functions directly from the measured polarizations and cross sections. A simultaneous fit of the cross sections, the recoil proton polarizations, and angular distributions of the polarized response functions will provide a determination of individual multipole amplitudes. Some of these multipole amplitudes are related to the concept of proton deformation. Both the recoil proton polarizations and polarized response functions were compared to two phenomenological models: MAID and SAID, which have all free parameters fixed, based on fits to previous world data. The measured helicity dependent observables, which are dominated by imaginary parts of \( \Delta \)(1232)-resonance excitation multipole amplitudes, agree very well with the two models. The measured helicity independent observables, which are dominated by real parts of background multipole amplitudes, do not agree completely with either model. These helicity independent observables are being measured accurately for the first time, giving new insight to the deformation of the proton and into reaction mechanisms of pion production.
Experiment Numbers: E91-011
Group: Hall A
Document: pdf
Accepted Manuscript:
Supporting Documents:
Supporting Datasets:
  • Data tables for JLab experiment e91011