Quasi-elastic polarization-transfer measurements on the deuteron in anti-parallel kinematics

We present measurements of the polarization-transfer components in the H-2((e) over right arrow, e'(p) over right arrow) reaction, covering a previously unexplored kinematic region with large positive (anti-parallel) missing momentum, p(miss), up to 220 MeV/c, and Q(2) = 0.65 (GeV/c)(2). These measurements, performed at the Mainz Microtron (MAMI), were motivated by theoretical calculations which predict small final-state interaction (FSI) effects in these kinematics, making them favorable for searching for medium modifications of bound nucleons in nuclei. We find in this kinematic region that the measured polarization-transfer components P-x and P-z and their ratio agree with the theoretical calculations, which use free-proton form factors. Using this, we establish upper limits on possible medium effects that modify the bound proton's form factor ratio G(E)/G(M) at the level of a few percent. We also compare the measured polarization-transfer components and their ratio for H-2 to those of a free (moving) proton. We find that the universal behavior of H-2, He-4 and C-12 in the double ratio (P-x/P-z)(A)/(P-x/P-z)(1H) is maintained in the positive missing-momentum region. (C) 2019 The Author(s). Published by Elsevier B.V.