2026/07/22 by BESIII Collaboration, M. Ablikim, M. N. Achasov +754
#hep-ex
A novel technique for measuring the spin polarization of final-state nucleons in a general-purpose spectrometer is validated. Using 10.09×109 J/ψ events at BESIII, the asymmetry of polarized proton scattering on detector support material is measured, and is consistent with the expected value. This proves that a general-purpose spectrometer can be utilized as a large-acceptance polarimeter, providing the spin polarization in addition to the conventional four-momentum information of the final-state particles. With this technique, physics capabilities are enhanced for existing and future facilities in particle and nuclear physics.