We present measurements of the electron helicity asymmetry in quasi-elastic proton knockout from 2H and 12C nuclei by polarized electrons. This asymmetry depends on the fifth structure function, is antisymmetric with respect to the scattering plane, and vanishes in the absence of final-state interactions, and thus it provides a sensitive tool for their study. Our kinematics cover the full range in off-coplanarity angle ϕpq, with a polar angle θpq coverage up to about 8°. The missing energy resolution enabled us to determine the asymmetries for knock-out resulting in different states of the residual 11B system. We find that the helicity asymmetry for p-shell knockout from 12C depends on the final state of the residual system and is relatively large (up to ≈0.16), especially at low missing momentum. It is considerably smaller (up to ≈0.01) for s-shell knockout from both 12C and 2H. The data for 2H are in very good agreement with theoretical calculations, while the predictions for 12C exhibit differences with respect to the data.

Original languageEnglish
Article number136798
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
StatePublished - 10 Jan 2022


FundersFunder number
Israel Academy of Arts and Sciences
National Science FoundationPHY-1812382, 2017630
National Science Foundation
Deutsche Forschungsgemeinschaft
United States-Israel Binational Science Foundation
Israel Science Foundation951/19, 390/15
Israel Science Foundation
Javna Agencija za Raziskovalno Dejavnost RSP1–0102
Javna Agencija za Raziskovalno Dejavnost RS
Hrvatska Zaklada za Znanost1680
Hrvatska Zaklada za Znanost
Ministry of Science and Technology, Israel
PAZY Foundation294/18
PAZY Foundation


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