Physics at the electron accelerator MAMI

Abstract

An overview of physics at the Mainz Microtron facility MAMI is given. After a short description of the essential parameters of the accelerator, selected results of three different collaborations A1, A2, and A3, each centered around one major experimental facility, are presented. The A1 collaboration has installed a setup of three large acceptance magnetic spectrometers. Results presented are high momentum components ( p m ≤ 700 MeV/ c) in 16 O( e, e′ p), L T separation and LT interference structure functions in p( e, e′ π +), and angular distribution of p( e, e′ p) π 0 at π 0 threshold. The A2 collaboration has installed a broad band tagger for experiments with nonpolarized and polarized photons. Results presented include p( γ, π + π 0) in the Δ(1232) P 33 region, p( γ, π 0 π 0) at threshold, p( γ, η) from threshold into the N(1535) S 11 resonance region, and a measurement of the E2 M1 ratio for the Δ(1232) P 33 resonance using polarized photons. The A3 collaboration has built a source of polarized electrons and a flexible setup to measure the 3 He( e, e′n) and d( e, e′ n) reaction in quasifree kinematics. From the asymmetries measured in these reactions a value for G E, n at q 2 = −0.31( GeV/ c) 2 is extracted. A forth collaboration A4 is setting up a large solid angle, high count rate liquid Xe calorimeter in order to investigate parity violating electron scattering.