Experiments on few-nucleon systems at MAMI

Abstract

The experimental effort at the Mainz Microtron with respect to few-body physics is focused on a number of selected topics. The structure of 3He has been studied in the reactions \(^3\vec{{\rm H}}{\rm e}(\vec{e},e{\prime}n)\) and \(^3\vec{{\rm H}}{\rm e}(\vec{e},e{\prime}p)\) with large (transversal) missing momenta and in quasi-elastic electron scattering. Experiments to determine the neutron electric form factor G en have been performed – a measurement at a four-momentum transfer Q 2 ∼ 1.5(GeV/c)2 took place in July 2007. Electromagnetically induced two-nucleon knockout has been investigated in order to study the role of correlated nucleon-nucleon motion in the nucleus. Measurements of the (e,e′ pn) reaction on 3He and 16O were performed for the first time. A triple-polarization experiment of type \(^3\vec{{\rm H}}{\rm e}(\vec{e},e{\prime}\vec{p})d\) has been performed in August 2007, where, in addition, the spin of the knocked-out proton is analyzed. This measurement provides information on the spin-dependent momentum distribution of proton-deuteron clusters in the 3He nucleus. By using this deuteron-tagging method spin-polarized 3He might also serve as an effective polarized proton target for electron scattering experiments.