Measurement of the neutron magnetic form factor from inclusive quasielastic scattering of polarized electrons from polarizedHe3

Abstract

We report a measurement of the asymmetry in spin-dependent quasielastic scattering of longitudinally polarized electrons from a polarized 3~e target. The neutron magnetic form factor G' ;, has been extracted from the measured asymmetry based on recent PWIA calculations using spin-dependent spectral functions. Our determination of G& at ~~= 0 . 1 9 (G~VIC)' agrees with the dipole parametrization. This experiment represents the first measurement of the neutron magnetic form factor using spin-dependent electron scattering. PACS nuniber(s): 25.30. Fj, 13.40.Gp, 14.20.Dh, 24.70.fs Electromagnetic form factors are of fundamental importance for an understanding of the underlying structure of nucleons. Knowledge of the distribution of charge and magnetization within the nucleons provides a sensitive test of models based on QCD, as well as a basis for calculations of processes involving the electromagnetic interaction with complex nuclei. Due to the lack of a free neutron target, the neutron electromagnetic form factors are known with less precision than the proton electric and magnetic form factors. They have been deduced in the past from elastic or quasielastic electron-deuteron scattering. This procedure involves considerable model dependence. The development of polarized targets and beams has allowed more complete studies of electromagnetic structure than has been possible with unpolarized reactions. In quasielastic scattering, the spin degrees of freedom introduce new response functions into the inclusive cross section, thus providing additional information on nuclear structure [I].3~e is an interesting nucleus for polarization studies because its ground state wave function is predominantly a spa- tially symmetric S state in which the spin of the nucleus is carried mainly by the unpaired neutron. Therefore, inelastic scattering of polarized electrons from polarized '~e in the vicinity of the quasielastic peak should be useful for studying the neutron electromagnetic form factors. This idea was first investigated by Blankleider and Woloshyn in closure approximation [2]. Friar et al. [3] have studied the model dependence in the spin structure of the 3~e wave function and its effect on the quasielastic asymmetry. Recently the plane wave impulse approximation (PWIA) calculations performed independently by two groups [4,5] using a spin-dependent spectral function show that the spin-dependent asymmetry is very sensitive to the neutron electric or magnetic form factors at certain kinematics near the top of the quasielastic peak. Two previous experiments [6,7] measured the spindependent asymmetry in quasielastic scattering of polarized electrons from oolarized h e . and demonstrated that this new experimental technique is feasible for studying the neutron electromagnetic structure. As a result, new experimental programs utilizing polarized electrons and polarized %e targets to study the neutron electromagnetic structure and the nucleon spin structure are under way at several electron accelerator laboratories (SLAC, MIT-B...

Neutron electromagnetic form factors and inclusive scattering of polarized electrons by polarized 3He and 3H targets

“…Eqs. (2) and (3)), with the most recent data from inclusive experiments that should be proportional, at qe peak, to R 3 He T ′ [5] and R 3 He T L ′ [6]. In Figs.…”

“…3(a) and 4(a) the theoretical predictions corresponding to: i) Av14 potential + Coulomb interaction, ii) RSCv8 potential + Coulomb interaction and iii) Paris potential without Coulomb interaction, from [9], are compared with the experimental data; it is worth noting that for the kinematics of Ref. [5], where A peak ∝ R 3 He T ′ , the asymmetry does not appreciably change by varying the two-body ISI (less than 2% at the qe peak), while for the kinematics of Ref. [6], where A peak ∝ R 3 He T L ′ , there is a little bit higher variation (less than 4% at the qe peak), in line with the findings of the theoretical analysis contained in [6].…”

“…3, the three-nucleon ground-state and the spin-dependent spectral functions we have adopted will be illustrated in detail; in Sect. 4, the comparison between our results, calculated by using different realistic twoand three-body interactions, and the most recent experimental values for 3 He asymmetries [5,6] will be presented, and em polarized responses at qe peak, for both 3 He and 3 H, will be investigated in detail up to Q 2 = 2 (GeV /c) 2 ; in Sect. 5, possible experiments for minimizing the model dependence in the extraction of neutron em form factors will be suggested; in Sect.…”

“…the D-wave, prevents the application of the naive picture and therefore also the polarized 3 He target is plagued by a non negligible proton contribution. In spite of this, many experimental efforts [3, 4,5,6] have been carried out with the aim of measuring the inclusive response of polarized 3 He at the quasielastic (qe) peak. Though such measurements were affected by sizable statistical and systematic uncertainties, a first estimate of the neutron magnetic form factor at Q 2 ≈ 0.2 (GeV /c) 2 [5] was extracted from the transverse polarized response (with a ≈ 20% accuracy), while no information on the charge form factor could be reliably obtained [6], due to the large proton contribution in the transverse-longitudinal polarized response.…”

“…In spite of this, many experimental efforts [3, 4,5,6] have been carried out with the aim of measuring the inclusive response of polarized 3 He at the quasielastic (qe) peak. Though such measurements were affected by sizable statistical and systematic uncertainties, a first estimate of the neutron magnetic form factor at Q 2 ≈ 0.2 (GeV /c) 2 [5] was extracted from the transverse polarized response (with a ≈ 20% accuracy), while no information on the charge form factor could be reliably obtained [6], due to the large proton contribution in the transverse-longitudinal polarized response. In order to improve the accuracy, in particular for the transverse polarized response, a new generation of inclusive experiments to be performed in the near future at TJNAF has been planned (see e.g.…”