Measurement of the helicity-dependent response in quasi-elastic proton knockout from $^{40}{\rm Ca}$
nucl-ex
/ Authors
Tim Kolar, Iris Sabo-Napadensky, Patrick Achenbach, Mirko Christmann, Michael Otto Distler, Luca Doria, Phillipp Eckert, Anselm Esser, Carlotta Giusti, Jennifer Geimer
and 27 more authors
Pepe Gülker, Matthias Hoek, Pascal Klag, Jechiel Lichtenstadt, Maximilian Littich, Theodoros Manoussos, David Markus, Harald Merkel, Miha Mihovilovič, Julian Müller, Ulrich Müller, Jonas Pätschke, Sebouh J. Paul, Eliezer Piasetzky, Saskia Plura, Joseph Pochodzalla, Matej Požun, Guy Ron, Björn Sören Schlimme, Concettina Sfienti, Sebastian Stengel, Ela Stephan,
/ Abstract
The role of the electron-helicity-dependent cross-section term and the structure function $f^{\prime}_{01}$ in the quasi-elastic $A(\vec{e}, e^{\prime}p)$ process was studied. The $f^{\prime}_{01}$ was measured for proton knockout from the $1\mathrm{d}_{3/2}$ shell in $^{40}\mathrm{Ca}$ via the $^{40}{\rm Ca}(\vec{e},e' p)^{39}{\rm K}_{\rm g.s.}$ reaction, leaving the residual nucleus in a well-defined state. It requires a longitudinally polarized electron beam and out-of-plane proton detection. This structure function vanishes in the absence of final-state interactions (FSI) involving the ejected proton. Presented are the dependencies of $f^{\prime}_{01}$ on the missing momentum (closely related to the initial proton's Fermi momentum) and the angle between the knocked-out proton and the virtual photon momenta. The role of the spin-orbit interaction in FSI through the $\vec{L}\cdot \vec{S}$ term in a nuclear optical potential is discussed.