Systematic study of the pp [FORMULA] pp[FORMULA] reaction
2010
A systematic study of the production of [FORMULA] -mesons in proton-proton collisions was carried out in a kinematically complete experiment at three excess energies ( [FORMULA] = 92, 128, 173 MeV). Both protons were detected using the large-acceptance COSY-TOF spectrometer at an external beam line at the Cooler Synchrotron COSY at Forschungszentrum Julich. The total cross-section, angular distributions of both [FORMULA] -mesons and protons were measured and presented in various reference frames such as the overall CMS, helicity and Jackson frame. In addition, the orientation of the [FORMULA] -spin and invariant-mass spectra were determined. We observe [FORMULA] -production to take place dominantly in Ss and Sp final states at [FORMULA] = 92, 128 MeV and, additionally, in Sd at [FORMULA] = 173 MeV. No obvious indication of resonant [FORMULA] -production via N * -resonances was found, as proton angular distributions are almost isotropic and invariant-mass spectra are compatible with phase space distributions. A dominant role of 3 P 1 and 1 S 0 initial partial waves for [FORMULA] -production was concluded from the orientation of the decay plane of the [FORMULA] -meson. Although the Jackson angle distributions in the [FORMULA] p-Jackson frame are anisotropic we argue that this is not an indication of a resonance but rather a kinematical effect reflecting the anisotropy of the [FORMULA] angular distribution. The helicity angle distribution in the [FORMULA] p-helicity frame shows an anisotropy which probably reflects effects of the [FORMULA] angular momenta in the final state; this observable may be, in addition to the orientation of the [FORMULA] decay plane, the most sensitive one to judge the validity of theoretical descriptions of the production process.
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