The determination of the neutron skin thickness of \ (^208 Pb\) from the PREX-II measurement of the parity-violating asymmetry \ (A ₕ\) has generated considerable discussion within the nuclear physics community, revealing notable discrepancies with previous experimental results and theoretical predictions. PREX also reported a beam-normal single-spin asymmetry \ (Aₙ\) for \ (^208 Pb\), a key background to \ (A ₕ\), that deviates from contemporary calculations — a discrepancy now known as the PREX anomaly. We present a new measurement of \ (Aₙ\) in elastic electron scattering from natural lead performed at MAMI and discuss its implications for solving the PREX anomaly. We also outline the concept of the forthcoming Mainz Radius EXperiment (MREX) at MESA, designed to deliver an independent measurement of \ (A ₕ\) in \ (^208 Pb\) with twice the precision of PREX-II. Abstract Published by the Jagiellonian University 2026 authors
Kozyrev et al. (Tue,) studied this question.
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