Summary of the seventh international symposium on meson-nucleon physics and the structure of the nucleon, MENU’97

Abstract

MENU’97 covered many stunning successes of chiral symmetry in intermediate energy reactions, especially of processes that involve pions. These successes include coupling constants, scattering lengths, threshold meson production, electric and magnetic polarizabilities of pions and nucleons, peripheral NN scattering, π, η and K decay rates and spectra. The πN data bank at low energy, which in the past was notorious for the inconsistencies of different data sets, is shown to become consistent by deleting a modest number of previously accepted data sub-sets. There is a consensus on a better value for the pion-nucleon coupling constant, which has been a bone of contention earlier, namely, fπNN2/4π=(75.4±0.4)×10−3 in satisfactory agreement with the Goldberger-Treiman relation. The mass-spin/parity distribution of the experimentally established πN resonances does not support the prediction of the harmonic oscillator type quark model. Some massive Δ++ resonances decay by η emission to the π+pη final state. In contrast to this the decay of massive N* states to π−pη in small, less than 5% of Δ++→π+pη. A new s-wave η decay has been identified, D33(1700)→P33(1232)+η. There is interesting new threshold data from CELSIUS on np→dη as well as on pp→ppη and np→npη.