Determination of the 27Al Neutron Distribution Radius from a Parity-Violating Electron Scattering Measurement

• Main Authors: Androić, Darko, Armstrong, D. S, Bartlett, K, Beminiwattha, R. S, Benesch, J, Benmokhtar, F, Birchall, J, Carlini, R. D, Cornejo, J. C, Covrig Dusa, S, Dalton, M. M, Davis, C. A, Deconinck, W, Dowd, J. F, Dunne, J. A, Dutta, D, Duvall, W. S, Elaasar, M, Falk, W. R, Finn, J. M, Forest, T, Gal, C, Gaskell, D, Gericke, M. T. W, Gray, V. M, Grimm, K, Guo, F, Hoskins, J. R, Jones, D. C, Jones, M. K, Kargiantoulakis, M, King, P. M, Korkmaz, E, Kowalski, S, Leacock, J, Leckey, J, Lee, A. R, Lee, J. H, Lee, L, MacEwan, S, Mack, D, Magee, J. A, Mahurin, R, Mammei, J, Martin, J. W, McHugh, M. J, Meekins, D, Mesick, K. E, Michaels, R, Micherdzinska, A, Mkrtchyan, A, Mkrtchyan, H, Narayan, A, Ndukum, L. Z, Nelyubin, V, Nuruzzaman, V, van Oers, W. T. H, Owen, V. F, Page, S. A, Pan, J, Paschke, K. D, Phillips, S. K, Pitt, M. L, Radloff, R. W, Rajotte, J. F, Ramsay, W. D, Roche, J, Sawatzky, B, Ševa, Tomislav, Shabestari, M. H, Silwal, R, Šimičević, Neven, Smith, G. R, Solvignon, P, Spayde, D. T, Subedi, A, Suleiman, R, Tadevosyan, V, Tobias, W. A, Tvaskis, V, Waidyawansa, B, Wang, P, Wells, S. P, Wood, S. A, Yang, S, Zang, P, Zhamkochyan, S, Christy, M. E, Horowitz, C. J, Fattoyev, F. J, Lin, Z
• Format: Journal Article
• Language: English
• Published: 2022
• Subjects: Fizika; PRIRODNE ZNANOSTI
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.128.132501

We report the first measurement of the parity- violating elastic electron scattering asymmetry on 27Al. The 27Al elastic asymmetry is A_PV = 2.16 +- 0.11 (stat) +- 0.16 (syst) ppm, and was measured at <Q^2> =0.02357 +- 0.0001 GeV^2, = 7.61 +- 0.02 degrees, and = 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 R_n = 2.89 +- 0.12 fm was determined using a many-models correlation technique. The corresponding neutron skin thickness R_n-R_p = -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 R_w = 3.00 +- 0.15 fm, and the weak skin thickness R_wk - R_ch = -0.04 +- 0.15 fm. The weak form factor at this Q^2 is F_wk = 0.39 +- 0.04.