Recoil polarization and beam-recoil double polarization measurement of η electroproduction on the proton in the region of the S₁₁(1535) resonance

The beam-recoil double polarization P_{x'}^h and P_{z'}^h and the recoil polarization P_{y'} were measured for the first time for the p(\vec{e},e'\vec{p})\eta reaction at a four-momentum transfer of Q^2=0.1 GeV^2/c^2 and a center of mass production angle of \theta = 120^\circ at MAMI C. With a center of mass energy range of 1500 MeV < W < 1550 MeV the region of the S_{11}(1535) and D_{13}(1520) resonance was covered. The results are discussed in the framework of a phenomenological isobar model (Eta-MAID). While P_{x'}^h and P_{z'}^h are in good agreement with the model, P_{y'} shows a significant deviation, consistent with existing photoproduction data on the polarized-target asymmetry.