Electroweak Measurements of Neutron Densities in CREX and PREX at JLab, USA

TL;DR

This paper discusses parity-violating electron scattering experiments at Jefferson Lab (PREX and CREX) that measure neutron densities in nuclei, providing insights into neutron skin thickness and nuclear forces.

Contribution

It reports on the implementation and results of PREX and CREX experiments, offering model-independent measurements of neutron distributions in ${}^{208}$Pb and ${}^{48}$Ca.

Findings

Neutron skin thickness in ${}^{208}$Pb measured.

Neutron density in ${}^{48}$Ca constrained.

Implications for neutron-rich matter properties.

Abstract

Measurement of the parity-violating electron scattering asymmetry is an established technique at Jefferson Lab and provides a new opportunity to measure the weak charge distribution and hence pin down the neutron radius in nuclei in a relatively clean and model-independent way. This is because the Z boson of the weak interaction couples primarily to neutrons. We will describe the PREX and CREX experiments on ${}^{208}$Pb and ${}^{48}$Ca respectively; these are both doubly-magic nuclei whose first excited state can be discriminated by the high resolution spectrometers at JLab. The heavier lead nucleus, with a neutron excess, provides an interpretation of the neutron skin thickness in terms of properties of bulk neutron matter. For the lighter ${}^{48}$Ca nucleus, which is also rich in neutrons, microscopic nuclear theory calculations are feasible and are sensitive to poorly constrained 3-neutron forces.