THE 3-SPECTROMETER FACILITY AT THE MAINZ MICROTRON MAMI

A set-up of three high-resolution magnetic spectrometers, for simplici ty named A, B and C, has been built as the central facility for the pr ecise determination of double and triple coincidence cross sections of hadron knock-out and meson production through the scattering of elect rons at the Mainz microtron MAMI. The spectrometers A and C with point -to-point optics in the dispersive plane and parallel-to-point optics in the non-dispersive plane have a solid angle of 28 msr and a momentu m acceptance of 20 and 25%, respectively. They each consist of a quadr upole, a sextupole and two dipole magnets, reaching maximum momenta of 735 and 550 MeV/c, respectively. The spectrometer B has a solid angle of 5.6 msr and a somewhat reduced momentum acceptance of 15%, but it reaches a maximum momentum larger than that of the MAMI electron beam (855 MeV/c). It consists of a single-clamshell dipole magnet with poin t-to-point optics in both planes. Each spectrometer is equipped with a position-sensitive detector system consisting of four planes of verti cal drift chambers, two planes of plastic scintillators and a threshol d gas Cherenkov detector. The operational experiences demonstrate that all three spectrometers exceed the specifications. Selected results o f double (e, e'x) and triple (e, e'x(1)x(2)) coincidence experiments, x(1) and x(2) standing for charged hadrons, are presented, which demon strate the performance of the whole set-up. (C) 1998 Elsevier Science B.V. All rights reserved.