Systematic study of the pp $ \rightarrow$ pp$ \omega$ reaction

A systematic study of the production of \( \omega\) -mesons in proton-proton collisions was carried out in a kinematically complete experiment at three excess energies ( \( \varepsilon\) = 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 \( \omega\) -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 \( \omega\) -spin and invariant-mass spectra were determined. We observe \( \omega\) -production to take place dominantly in Ss and Sp final states at \( \varepsilon\) = 92, 128 MeV and, additionally, in Sd at \( \varepsilon\) = 173 MeV. No obvious indication of resonant \( \omega\) -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 3P1 and 1S0 initial partial waves for \( \omega\) -production was concluded from the orientation of the decay plane of the \( \omega\) -meson. Although the Jackson angle distributions in the \( \omega\) 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 \( \omega\) angular distribution. The helicity angle distribution in the \( \omega\) p-helicity frame shows an anisotropy which probably reflects effects of the \( \omega\) angular momenta in the final state; this observable may be, in addition to the orientation of the \( \omega\) decay plane, the most sensitive one to judge the validity of theoretical descriptions of the production process.