CONSTRAINTS ON NEUTRON-STAR RADII FROM LABORATORY EXPERIMENTS

High-precision measurements of asymmetry in parity-violating electron- nuclei scattering experiments enhance our understanding of the structure of nuclei and neutron stars. PREX-2 and CREX (Lead/Calcium Radius Ex-periments) are two recent experiments conducted at JLab in Newport News, Virginia, USA, by elastically scattering an electron beam with rapidly flip-ping helicity from 208Pb and 48Ca targets, respectively. PREX-2 measured an asymmetry A208 PV = 550 +/- 16 [stat.] +/- 8 [sys.] ppb at kinematics with mean Q2 similar to 0.00616 GeV2. Together with the predecessor PREX-1 , it con-strained the 208Pb neutron skin to R208 skin = 0.283 +/- 0.071 fm. The combined constraint on nuclear DFT models from PREX and the NICER telescope neutron-star radii measurements is in similar to 1 standard deviation tension with the constraint from the LIGO tidal deformability measurements. CREX was conducted at kinematics with mean Q2 similar to 0.0297 GeV2 , resulting in an asymmetry A48PV = 2668 +/- 106 [stat.] +/- 40 [sys.] ppb and the 48Ca neu-tron skin R48 skin = 0.121 +/- 0.026 [exp.] +/- 0.024 [model] fm respectively. The CREX result contrasts the PREX result by predicting a thinner neutron skin for medium-mass nuclei compared to heavy nuclei. Understanding these anomalies with further studies is necessary to pin down the density -dependence of nuclear symmetry energy and constrain neutron-star radii accurately.