Measurements of the electron-helicity asymmetry in the quasi-elastic $\mathrm{A}(\vec{e},e^{\prime }p)$ process

Abstract

We present measurements of the electron helicity asymmetry in quasi-elastic proton knockout from ${}^2$H and ${}^{12}$C 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 ${\varphi }_{pq}$, with a polar angle ${\theta }_{pq}$ coverage up to about 8 degrees. The missing energy resolution enabled us to determine the asymmetries for knock-out resulting in different states of the residual ${}^{11}$B system. We find that the helicity asymmetry for $p$-shell knockout from ${}^{12}$C depends on the final state of the residual system and is relatively large (up to $\approx 0.16$), especially at low missing momentum. It is considerably smaller (up to $\approx 0.01$) for $s$-shell knockout from both ${}^{12}$C and ${}^2$H. The data for ${}^2$H are in very good agreement with theoretical calculations, while the predictions for ${}^{12}$C exhibit differences with respect to the data.

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Cited by in corpus (2)

• Measurement of ${}^6\mathrm{H}$ ground state energy in an electron scattering experiment at MAMI-A1
• Electron and neutrino scattering off the deuteron in a relativistic framework