Measurements of the induced polarization in the quasi-elastic A(e,e′p→) process in non-coplanar kinematics

Abstract We report measurements of the induced polarization P → of protons knocked out from 2H and 12C via the A ( e , e ′ p → ) reaction. We have studied the dependence of P → on two kinematic variables: the missing momentum p miss and the “off-coplanarity” angle ϕ p q between the scattering and reaction planes. For the full 360° range in ϕ p q , both the normal ( P y ) and, for the first time, the transverse ( P x ) components of the induced polarization were measured with respect to the coordinate system associated with the scattering plane. P x vanishes in coplanar kinematics, however in non-coplanar kinematics, it is on the same scale as P y . We find that the dependence on ϕ p q is sine-like for P x and cosine-like for P y . For carbon, the magnitude of the induced polarization is especially large when protons are knocked out from the p 3 / 2 shell at very small p miss . For the deuteron, the induced polarization is near zero at small | p miss | , and its magnitude increases with | p miss | . For both nuclei such behavior is reproduced qualitatively by theoretical results, driven largely by the spin-orbit part of the final-state interactions. However, for both nuclei, sizeable discrepancies exist between experiment and theory.