Physics at MAMI

Abstract

The Mainz Microtron MAMI has delivered a high quality electron beam with maximum energy of 880MeV for many years. Recently the MAMI C stage with its maximum energy of 1.5GeV was put into operation successfully and is delivering beam routinely now. The A1 collaboration is doing electron scattering experiments with a “Three Spectrometer Setup”. A first experiment using the MAMI C beam to measure the “Recoil polarisation and beam-recoil double polarisation of eta electroproduction on the proton in the region of the S11(1535) resonance” has been finished. A new, very compact magnetic spectrometer (KaoS) suitable especially for the detection of kaons is being installed now. The A2 collaboration is measuring photon absorption cross section using circularly and linearly polarized photons up to an energy of 1.4GeV. The photons are produced in the Bremsstrahlung process. In the framework of the international GDH collaboration we have measured the photoabsorption cross sections of circularly polarized photons on longitudinally polarized protons to determine for the first time the helicity dependence of the total cross section and of the partial reaction channels in a large kinematical range, which provides new information about the excitation spectrum of the nucleon. The experiment was done at MAMI B (Mainz) for photon energies up to 800MeV and at ELSA (Bonn) for the high energy range up to 3GeV. In the years 2005/2006 the Crystal Ball detector with its unique capability to cope with multi photon final states was set up and used with polarized beams and unpolarized targets in Mainz. The experimental apparatus will be completed by polarized targets and a recoil polarimeter.

For the CBall@MAMI and A2 Collaborations