Experiments with Longitudinally Polarized Electrons in a Storage Ring Using a Siberian Snake

Abstract

We report on first measurements with polarized electrons stored in a medium-energy ring and with a polarized internal target. Polarized electrons were injected at 442 MeV (653 MeV), and a partial (full) Siberian snake was employed to preserve the polarization. Longitudinal polarization at the interaction point and polarization lifetime of the stored electrons were determined with laser backscattering. Spin observables were measured for electrodisintegration of polarized 3 He, with simultaneous detection of scattered electrons, protons, neutrons, deuterons, and 3 He nuclei, over a large phase space.PACS numbers: 24.70. + s, 25.30.Fj, 29.20.Dh, 29.27.Hj In the scattering of leptons from hadronic targets, the leptonic part of the interaction is well understood, allowing one to focus on the strong-interaction vertex and the underlying structure and dynamics of the nucleus. The ultimate probe consists of spin-dependent scattering with polarized leptons and polarized targets [1], and the last decade has seen a large effort devoted to the realization of such experiments.Most experiments used electrons beams impinging on external polarized targets to achieve adequate luminosity. In this way, data on, e.g., the neutron form factors and deep-inelastic structure functions have been obtained (see, e.g., [2][3][4][5][6][7]). Although typically lower in luminosity, spindependent electron scattering experiments from polarized gas targets internal to storage rings have the advantages: (i) they can be well matched with the use of large-acceptance detectors; (ii) rapid polarization reversal and flexible orientation of the nuclear target spin can be obtained, reducing systematical uncertainties; (iii) low-energy recoiling particles can escape the ultrathin targets and can be detected, allowing a complete reconstruction of the final state in the electrodisintegration of few-body systems. So far, electromagnetic spin-correlation observables from internal gas target experiments have been obtained only at DESY [7] in the deep-inelastic scattering regime. There the electron beam energy is high enough that transverse polarization builds up through the Sokolov-Ternov effect [8].For a study of nuclear structure and dynamics in both the quasifree scattering and D-resonance region, electron beams with energies up to 1 GeV are optimal: one may achieve resolutions in energy and momentum sufficient to distinguish various nuclear states and details in the wave functions; one can keep the momentum transfer small to optimize the sensitivity to long-distance nucleon and nuclear physics effects, while detection of heavily ionizing recoiling nuclear particles yields increased sensitivity to coherent effects in the nuclear dynamics. However, for such low electron beam energies the self-polarizing time is too long to take advantage of, and one has to inject polarized electrons and rely on Siberian-snake techniques. An experiment with the VEPP-2M collider at BINP, Novosibirsk [9], demonstrated that with such a solenoid (i.e., snake) the polarization...

Measurement of double-polarization asymmetries in the quasi-elastic He→3(eMihovilovič1, Gao2, Long3 et al. 2019Physics Letters B6020View full textAdd to dashboardCite

“…Such measurements have been extremely scarce. A single asymmetry data point with high uncertainty exists from NIKHEF [9,10]. In addition, we have a precise measurement of both transverse and longitudinal asymmetries separately for the 2bbu and 3bbu channels in quasi-elastic kinematics [11,12], but the measurement was restricted to (and summed over) relatively low p m .…”

Measurement of Double-Polarization Asymmetries in the QuasielasticHe→3(e<

“…ðẽ; e 0 pÞpn and 3 He ! ðẽ; e 0 pÞd channels have been studied at NIKHEF [8,9] and Mainz [10,11], but no published data on the polarized 3 He ! ðẽ; e 0 dÞ exist, chiefly due to the fact that previous experiments, though attempted, lacked present-day highly polarized beams and targets, which resulted in poor experimental figures-of-merit and prohibitive uncertainties.…”