Physical Review Letters
We report the first measurement of the parity-violating elastic electron scattering asymmetry on 27Al. The 27Al elastic asymmetry is APV=2.16±0.11(stat)±0.16(syst) ppm, and was measured at ⟨Q2⟩=0.02357±0.00010 GeV2, ⟨θlab⟩=7.61°±0.02°, and ⟨Elab⟩=1.157 GeV with the Qweak apparatus at Jefferson Lab. Predictions using a simple Born approximation as well as more sophisticated distorted-wave calculations are in good agreement with this result. From this asymmetry the 27Al neutron radius Rn=2.89±0.12 fm was determined using a many-models correlation technique. The corresponding neutron skin thickness Rn−Rp=−0.04±0.12 fm is small, as expected for a light nucleus with a neutron excess of only 1. This result thus serves as a successful benchmark for electroweak determinations of neutron radii on heavier nuclei. A tree-level approach was used to extract the 27Al weak radius Rw=3.00±0.15 fm, and the weak skin thickness Rwk−Rch=−0.04±0.15 fm. The weak form factor at this Q2 is Fwk=0.39±0.04.
Androic, D.; Armstrong, David S.; and al., et, Determination of the ^27Al Neutron Distribution Radius from a Parity-Violating Electron Scattering Measurement (2022). Physical Review Letters, 128(13).
This work is made available for educational and personal use only. Copyright is credited to the authors. Any other uses should be directed to the publisher.