Precision Determination of the Neutral Weak Form Factor of Ca 48

We report a precise measurement of the parity-violating (PV) asymmetry APV in the elastic scattering of longitudinally polarized electrons from Ca48. We measure APV=2668±106(stat)±40(syst) parts per billion, leading to an extraction of the neutral weak form factor FW(q=0.8733 fm-1)=0.1304±0.0052(stat)±0.0020(syst) and the charge minus the weak form factor Fch-FW=0.0277±0.0055. The resulting neutron skin thickness Rn-Rp=0.121±0.026(exp)±0.024(model) fm is relatively thin yet consistent with many model calculations. The combined CREX and PREX results will have implications for future energy density functional calculations and on the density dependence of the symmetry energy of nuclear matter.