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Determination of the ^27Al Neutron Distribution Radius from a Parity-Violating Electron Scattering Measurement
Androic, D. Armstrong, David S.
Androic, D.
Armstrong, David S.
Abstract
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.
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2022-04-01
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Physics
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https://doi.org/10.1103/PhysRevLett.128.132501