MREX@MAMI

Transverse Asymmetry Measurements on ²⁰⁸Pb

The beam-normal single spin asymmetry of ²⁰⁸Pb will be measured at MAMI at two different beam energies in the energy regime of the future MESA accelerator. These data will allow on one side to benchmark the energy dependence of the beam-normal single spin asymmetry in the theoretical treatment. Together with the new measurement of A_n for ²⁰⁸Pb by the PREX-II experiment at substantially higher energy, they might provide on the other side additional clues to the solution of the current tension.

Determination of the Surface Thickness of ²⁰⁸Pb

For the first time the surface thickness of ²⁰⁸Pb will be determined in parity-violation electron scattering at MAMI. Because of the current model uncertainty of 25% the precision in both the PREX-II and MESA neutron-skin determinations will be limited by this uncertainty. An independent 10% measurement of the surface thickness will reduce this
contribution to a level below the error budget of the parity-violation asymmetry measurement.
These data will thus remove the dominant model dependence in the method and together with the newest PREX-II data they will provide the most stringent model independent measurement of the neutron-skin thickness in ²⁰⁸Pb. This will pave the way to the most precise determination of the neutron-skin thickness at MESA.