D. Eyl

Electromagnetic form factors of the nucleon

Abstract The internal structure of proton and neutron is manifested in a variety of observables. The form factors for elastic electron scattering which describe the distribution of charge and magnetic moments provide information vital for our understanding of the confined quark system. The form factors of the proton could be measured over a wide range of momentum transfer through the conventional method of Rosenbluth separation. The determination of the neutron form factors is more demanding; it will now benefit from coincidence experiments at modern cw accelerators. For the neutron charge form factor a measurement of the asymmetry in the scattering of high energy polarised electrons from polarised targets or the spin transfer to the recoiling neutron from unpolarised targets promises a big improvement. Experiments of this type have already been started and deliver first results.

Determination of the neutron electric formfactor in quasielastic collisions of polarized electrons with 3He and 2D. Collaboration A3 at MAMI

The determination of the neutron electric formfactor from quasielastic reactions 3H↘e(e↘,e′n) and D(e↘,e′,n↘) respectively is one of the present goals of experiments with polarized electrons at the Mainz race track microtron MAMI. A GaAsP‐photoelectron source is used at MAMI to get an 855 MeV electron beam spinpolarized to a degree of 35% at a current of 10 μA. Polarized 3He‐nuclei are produced by optical pumping metastable 3He. Scattered electrons are detected in coincidence with the recoil neutrons, the transverse spinpolarization of the neutrons may be analyzed by neutron‐proton scattering in a double wall plastic scintillator detector. A subset of the final detector set‐up has been tested successfully now by investigating the polarization transfer to the proton in reactions H(e↘,e′p↘) and D(e↘,e′p↘) and to the neutron in D(e↘,e′n↘) at a 4‐momentum transfer with −Q2=8fm−2. First data from the exclusive quasielastic collision 3H↘e(e↘,e′n) indicate a value of the neutron electric formfactor of GnE=0.035±...

First measurement of the electric formfactor of the neutron in the exclusive quasielastic scattering of polarized electrons from polarized 3He

A first measurement of the asymmetry in quasielastic scattering of longitudinally polarized electrons from a polarized 3He gas target in coincidence with the knocked out neutron is reported. This measurement was made feasible by the cw beam of the 855 meV Mainz Microtron MAMI. It allows a determination of the electric formfactor of the neutron GnE independent of binding effects to first order. At Q2=0.31 (GeV/c)2 two asymmetries A∥(S↘He∥q↘) and A⊥(S↘He⊥q↘) have been measured giving A∥=(−7.40±0.73%) and A⊥=(0.89±0.30)%. The ratio A⊥/A∥ is independent of the absolute value of the electron and target polarization and yields GnE=0.035±0.012±0.005.

Determination of the neutron electric form factor GEn in double polarized electron scattering from 3He

The neutron electric form factor GEn has been measured at the cw electron accelerator MAMI in the double polarized exclusive reactions 3He(e,e′n) and D(e,e′n) in quasi elastic kinematics with one common detector system. Experimental set-up and analysis of a 3He(e,e′n)-measurement in the range of momentum transfer Q2=0.27−0.5 (GeV/c)2 are discussed in this article. For events with low missing momentum (|Pm|⩽100 MeV/c) the PWIA analysis yields GEn=0.0352±0.0033±0.0024 with statistical and systematical error, corresponding to a quadratically added total error of 11.6% relativ. This result will be compared with preliminary results obtained from the D(e,e′n)-reaction and with data from elastic D(e,e′) scattering.

The Electric Formfactor of the Neutron Determined by Quasielastic Scattering of Longitudinally Polarized Electrons from 3He and 2D

The recent availability of polarized electron beams at electron accelerator laboratories adds another technique to probing the electromagnetic structure of nuclear matter [1]. The present paper discusses the application of polarized electron scattering to the determination of the electric formfactor of the neutron. Its value at medium energies is only poorly known hitherto. Electron scattering is dominated by interaction with the neutron magnetic moment. Therefore the contribution of the charge distribution to the scattering cross section is scarcely detectable in case of unpolarized collision partners. The elastic scattering of longitudinally polarized electrons from a polarized neutron target offers a new and better chance to measure the neutron electric formfactor.