Near-Threshold Meson Production in Proton-Proton Collisions


In the present paper, results of experimental studies of near-threshold meson production in the reactions
pp->d pi+, pp->pp eta', pp->pK+Lambda, and pp->ppK+K-
are presented. The experiments were performed at the new cooler synchrotron COSY-Jülich. The first of the above reactions was measured by using the external magnetic spectrometer BIG KARL, and the three remaining reactions were studied at the internal COSY-11 facility, resulting in the first world data on near-threshold cross sections in these reactions. In both experiments, the magnetic field of dipole magnets was used for separating the ejectiles from the beam and for reconstructing their momentum vectors at the target point. This experimental method allowed measurements with high detection acceptance very close to threshold, at excess energies of the order of 1 MeV. At higher energies, detection efficiency was drastically limited by the height of the gaps in dipole magnets. Particle trajectories were measured with built in Cracow drift chambers and, in the off line analysis, they were traced back through the magnetic field to the target which allowed us to determine the momentum vectors at the target point. Particle identification proceeded via the time-of-flight measurement combined with the information on particle momenta. The missing-mass method was applied to identify unobserved ejectiles. High missing-mass resolution, achieved thanks to precise particle momenta reconstruction, allowed us to extract signals of the measured reaction from the background of other possible processes, even for reaction cross sections at the level of 1 nbarn.

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