At medium energy proton storage rings with phase space cooling, IUCF in Bloomington, CELSIUS in Uppsala and COSY in Jülich, the production of mesons near threshold has been subject of detailed studies during the last years. Experimental data obtained at complementary facilities provide access to both the underlying reaction mechanisms and the structure of mesons and baryons.
The COoler SYnchrotron at the Forschungszentrum Jülich delivers a phase space cooled beam with proton energies up to 2.6 GeV using both electron and stochastic cooling. At present, beam intensities of 4*1010 stored protons are provided. The high quality beam with a relative momentum resolution dp/p <= 10-4 and emittances epsilon <= 1 pi mm mrad serves internal and external experiments.
The COSY-11 installation is an internal facility at COSY designed for threshold meson production studies. Close to threshold only few partial waves contribute to the scattering amplitudes, which simplifies the theoretical interpretation. Due to low relative velocities of the ejectiles and, consequently, extended interaction times, effects of low energy baryon-baryon, meson-baryon and meson-meson final state interaction have a strong effect on the measured observables. At the same time, a large momentum transfer probes the short range part of the nucleon-nucleon force.
Experimentally, due to small transverse momenta, close to threshold all ejectiles are limited to a narrow forward cone in the laboratory system. A high geometrical acceptance is attainable with a comparatively small detector setup.
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Publication: Nucl.Phys.News 9 (1999) 27-32