Single-spin asymmetries in the elastic electron-proton scattering and the strange-quark contributions to the form factor of the nucleon

The A4 collaboration at the MAMI accelerator facility in Mainz investigates the structure of the proton by elastic scattering of polarized electrons off unpolarized hydrogen. At longitudinal polarization there is a parity violating asymmetry in the cross section which gives information about the contribution of strangeness to the vector form factor of the proton. At transverse polarization there are azimuthal asymmetries, which arise from the contribution of two-photon exchange to the cross section and allow access to the imaginary part of the two-photon amplitude. Within the scope of this thesis, measurements have been made and analyzed at two momentum transfers both with longitudinal and transverse polarization. The main emphasis has been placed on the extraction of the raw asymmetries out of the data, the corrections of the raw asymmetries for false asymmetries, the estimation of the systematic errors and the determination of the strange form factors out of the parity violating asymmetries. For the measurements at longitudinal polarization, the asymmetries have been determined to A=(-5.59±0.57stat±0.29syst) ppm at Q2=0.23 (GeV/c)2 and A=(-1.39±0.29stat±0.12syst) ppm at Q2=0.11 (GeV/c)2. The linear combination of the strange form factors have been evaluated to GEs+0.225GMs=0.029±0.034 and GEs+0.106GMs=0.070±0.035 respectively. Both results are in agreement with other experiments and suggest a nonvanishing contribution of strangeness to the form factors. For the measurements at transverse polarization the normal spin asymmetries have been determined to A=(-8.51±2.31stat±089syst) ppm at E=855 MeV and Q2=0.23 (GeV/c2) and to A=(-8.59±0.89stat±0.83syst) ppm at E=569 MeV and Q2=0.11 (GeV/c)2. The size of the asymmetries prove that not only the ground state of the proton but also excited states contribute to the intermediate hadronic state. (Orig.)