PAPER / ARXIV:2609.07518
PREX Collaboration : D. Adhikari (1 and 2 and 3), H. Albataineh (4), D. Androić (5), K.A. Aniol (6), D.S. Armstrong (7), T.D. Averett (7), C. Ayerbe Gayoso (7), S.K. Barcus (8), V. Bellini (9), R.S. Beminiwattha (10), J.F. Benesch (8), H. Bhatt (11), D. Bhatta Pathak (10), D. Bhetuwal (11), B. Blaikie (12), J.A. Boyd III (13), Q. Campagna (7 and 11), A. Camsonne (8), G.D. Cates (13), Y. Chen (10), C. Clarke (8), J.C. Cornejo (14), S. Covrig Dusa (8), M. M. Dalton (8), P. Datta (15), A. Deshpande (16 and 17 and 18), D. Dutta (11), E. Fuchey (15), C. Gal (8), D. Gaskell (8), M. Gericke (12), C. Ghosh (8 and 19 and 16), I. Halilovic (12), J.-O. Hansen (8), O. Hassan (20), F. Hauenstein (8), W. Henry (8 and 21), C.J. Horowitz (22), C. Jantzi (13), S. Jian (13), S. Johnston (19), D.C. Jones (21 and 8), S. Kakkar (12), B. Karki (23), S. Katugampola (13), C. Keppel (8), P.M. King (23), D.E. King (21), K.S. Kumar (19 and 16), T. Kutz (16), N. Lashley-Colthirst (24), G. Leverick (12), H. Liu (8 and 19), N. Liyanage (13), S. Malace (8), J. Mammei (12), R. Mammei (25), M. McCaughan (8), D. McNulty (1), D. Meekins (8), C. Metts (7), R. Michaels (8), M. Mihovilovic (26 and 27), M.M. Mondal (16, and 17), J. Napolitano (21), A. Narayan (28), D. Nikolaev (21), V.F. Owen (7), C. Palatchi (22), J. Pan (12), B. Pandey (24 and 29), S. Park (8 and 11 and 16), K.D. Paschke (13), M. Petrusky (30), M.L. Pitt (2), S. Premathilake (13), A.J.R. Puckett (15), B. Quinn (14), R. Radloff (23), S. Rahman (12 and 18), A. Rathnayake (13), B.T. Reed (31), P.E. Reimer (32), R. Richards (16), S. Riordan (32), Y.R. Roblin (8), S. Seeds (15), A. Shahinyan (33), P. Souder (34), L. Tang (8 and 24), M. Thiel (35), Y. Tian (34), G.M. Urciuoli (36), E.W. Wertz (7), B. Wojtsekhowski (8), T. Ye (16), A. Yoon (37), W. Xiong (34 and 38), A.J. Zec
RESUMO
We have measured the parity-violating elastic electron scattering asymmetry in the PREX and CREX experiments on ${}^{208}$Pb and ${}^{48}$Ca respectively; these are both doubly-magic nuclei whose excited states can be discriminated from the ground state by the high resolution spectrometers in Hall A at Jefferson Lab. This asymmetry provides a precise determination of the weak charge form factor at one $Q^2$ and pins down the neutron radius in these two nuclei in a relatively clean and model-independent way. This is because the $Z^0$ boson of the weak interaction couples primarily to neutrons. The heavier lead nucleus, with a neutron excess, provides an interpretation of the neutron skin thickness in terms of properties of bulk neutron matter. For the lighter ${}^{48}$Ca nucleus, which is also rich in neutrons, comparisons to microscopic nuclear theory calculations are sensitive to poorly constrained 3-neutron forces. The weak neutral form factors $F_W(Q^2)$ were extracted to be $0.368 \pm 0.013$ at $Q = 0.3977 {\rm\ fm}^{-1}$ for $^{208}$Pb from PREX-2 and $0.1304 \pm 0.0055$ at $Q = 0.8733 {\rm\ fm}^{-1}$ for $^{48}$Ca. The form factor differences $(F_{ch}-F_W)(Q^2)$ were calculated to be $0.041 \pm 0.013$ at $Q = 0.3977 {\rm fm}^{-1}$ for $^{208}$Pb from PREX-2 and $0.0277 \pm 0.0055$ at $Q = 0.8733 {\rm fm}^{-1}$ for $^{48}$Ca. Correcting for Coulomb distortions and using nuclear model information, we find the neutron skin thicknesses to be $R^{208}_{\rm skin} = 0.283 \pm 0.071$ fm combining PREX-1 and PREX-2 and $R^{48}_{\rm skin} = 0.121 \pm 0.035$ fm. This paper provides a full description of the special experimental and data analysis techniques employed for precisely measuring these small asymmetries.
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