Some of the important results from the COSY-Juelich spin programme are summarised. These include the measurement of the deuteron beam momentum through the excitation of a depolarising resonance, which allowed the mass of the eta-meson to be determine
d to high precision. The charge exchange of polarised deuterons on hydrogen gave rise to a detailed study of the spin dependence of large angle neutron-proton elastic scattering amplitudes. The measurements of the cross section and analysing powers for pion production in both pp and pn collisions at 353 MeV could be described very successfully in terms of a partial wave decomposition.
The cross section for inclusive multipion production in the pp->ppX reaction was measured at COSY-ANKE at four beam energies, 0.8, 1.1, 1.4, and 2.0 GeV, for low excitation energy in the final pp system, such that the diproton quasi-particle is in th
e 1S0 state. At the three higher energies the missing mass Mx spectra show a strong enhancement at low Mx, corresponding to an ABC effect that moves steadily to larger values as the energy is increased. Despite the missing-mass structure looking very different at 0.8 GeV, the variation with Mx and beam energy are consistent with two-pion production being mediated through the excitation of two Delta(1232) isobars, coupled to S-- and D-- states of the initial pp system.
