MREX: Mainz Radius Experiment

• Applicant: Professorin Dr. Concettina Sfienti
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 454637981

The Equation of State (EoS) is a fundamental property of nuclear matter that describes the relationships between energy, pressure, temperature, density, and neutron-proton asymmetry. Despite being 18 orders of magnitude different in size, nuclei and neutron stars are governed by the same physics enshrined in the EoS. In particular, the neutron-skin thickness of heavy nuclei is strongly correlated to the poorly-known slope of the symmetry energy at saturation density. In spite of the mounting experimental effort to determine the neutron-skin thickness of heavy nuclei, a precise determination remains elusive.The extraction of the neutron-skin thickness in parity-violation experiments is based on the measurement of the weak form factor at a single value of momentum transfer. Thus some assumptions concerning the surface thickness have to be made in order to reliably extract the neutron-skin thickness. In addition, the puzzling observation of a zero transverse asymmetry in 208Pb from the PREX collaboration is still a matter of debate both because of the implications for false asymmetries contributing substantially to the total systematic error of the neutron-skin measurement, and because of the apparent failing of the theoretical predictions of such contributions.In view of the expected growing number of gravitational wave measurements of neutron star mergers from LIGO and Virgo, the new astronomical observations on neutron star radii of NICER, and the planning for the ultimate measurement of neutron-skin thickness at MESA, it becomes imperative to thoroughly investigate the methodology to extract the neutron skin from parity violation.The goals of the of project will be: *) Transverse Asymmetry Measurements on 208PbThe beam-normal single spin asymmetry of 208Pb will be measured at the MAMI accelerator at two different beam energies in the energy regime of the future MESA accelerator. **) Determination of the Surface Thickness of 208PbFor the first time the surface thickness of 208Pb will be determined in parity-violation electron scattering at the MAMI accelerator. These data will remove the dominant model dependence in the method to extract the neutron-skin thickness from parity violation experiments.

• DFG Programme: Research Grants