Hadronic threshold reactions
IKP-I, Forschungszentrum Jülich, D-52425, Jülich, Germany
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First investigations on meson production at threshold in the strong interaction began in the fifties when sufficient energies of accelerated protons were available. Early experiments performed with bubble chambers revealed already typical ingredients of threshold studies, which were superseded by more complete meson production investigations at the nucleon beam facilities TRIUMF, LAMPF, PSI, LEAR and SATURNE. Currently, at the cooler rings IUCF, CELSIUS and COSY the field is entering a new domain of precision and further progress. The analysis of this new data in the short-range limit permits a more fundamental consideration and a quantitative comparison of the production processes for different mesons in the few-body final states. The interpretation of the data takes advantage of the fact that production reactions close to threshold are characterized by only a few degrees of freedom between a well-defined combination of initial and exit channels. Deviations from predictions of phase-space-controlled one-meson exchange models are indications of new physics. Precision data on differential cross-sections, isospin and spin observables --partly but by no means adequately available-- are presently turning up.
© Società Italiana di Fisica and Springer-Verlag, 2003