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

Abstract

We present measurements of the polarization-transfer components in the 2 H( e, e p) 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 2 H to those of a free (moving) proton. We find that the universal behavior of 2 H, 4 He and 12 C in the double ratio (Px/Pz) A (Px/Pz) 1 H is maintained in the positive missing-momentum region.

Measurements of the electron-helicity asymmetry in the quasi-elastic A(e→,e′p)<

“…These two methods of beampolarization measurement produced mutually consistent results as described in [12,13,15,16]. The target used for the 2 H measurements was a 50 mm long oblong cell filled with liquid deuterium [11][12][13] while the 12 C target consisted of three 0.8 mm-thick graphite foils [14][15][16]. We also performed calibration runs using a liquidhydrogen target.…”

“…The beam polarization was measured periodically with a Møller polarimeter [22,23], and verified by a Mott polarimetry measurement [24]. These two methods of beampolarization measurement produced mutually consistent results as described in [12,13,15,16]. The target used for the 2 H measurements was a 50 mm long oblong cell filled with liquid deuterium [11][12][13] while the 12 C target consisted of three 0.8 mm-thick graphite foils [14][15][16].…”

“…A series of measurements of the A( e, e p) reaction was performed at the Mainz Microtron (MAMI) using 2 H and 12 C targets. The polarization transfer to the knock-out proton was measured to investigate the properties of deeply bound (highly off-mass-shell) protons in the nucleus [11][12][13][14][15][16]. In search of deviations of the form factors of a bound proton from the free proton ones these measurements have been compared to calculations which are sensitive to this ratio.…”

Report on scipost_201910_00013v1

“…Scattered electrons were detected in the high-resolution spectrometer (HRS) and knocked-out neutrons were detected using the Hall A Neutron Detector (HAND) [14,15]. This experiment ran concurrently with multiple experiments that measured quasi-elastic structure on polarized 3 He [16,17,18,19]. The 3 He target was polarized through spin-exchange optical pumping (SEOP) [20,21,22,23,24].…”

“…The ratios (3) for three nuclei ( 2 H, 4 He and 12 C) measured at TJNAF and MAMI (see [18] and references therein), shown as functions of ν, are shown in Fig. 7.…”