Measurements of the electron-helicity asymmetry in the quasi-elastic \({\rm A}(\vec{e},e' p)\) process

• Published in: arXiv.org
• Main Authors: Kolar, Tim, Paul, Sebouh J, Achenbach, Patrick, Arenhövel, Hartmuth, Ashkenazi, Adi, Beričič, Jure, Böhm, Ralph, Bosnar, Damir, Brecelj, Tilen, Cline, Ethan, Cohen, Erez O, Distler, Michael O, Esser, Anselm, Friščić, Ivica, Gilman, Ronald, Giusti, Carlotta, Heilig, Matthias, Hoek, Matthias, Izraeli, David, Kegel, Simon, Klag, Pascal, Korover, Igor, Lichtenstadt, Jechiel, Mardor, Israel, Merkel, Harald, Middleton, Duncan G, Mihovilovič, Miha, Müller, Julian, Müller, Ulrich, Mor Olivenboim, Piasetzky, Eliezer, Pochodzalla, Josef, Guy, Ron, Schlimme, Björn S, Schoth, Matthias, Schulz, Florian, Sfienti, Concettina, Širca, Simon, Spreckels, Rouven, Štajner, Samo, Stöttinger, Yvonne, Strauch, Steffen, Thiel, Michaela, Tyukin, Alexey, Weber, Adrian, Israel, Yaron
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 01.07.2021
• Subjects: Asymmetry; Coplanarity; Energy resolution; Helicity; Kinematics; Physics - Nuclear Experiment
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2107.00763

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 \(\phi_{pq}\), 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.