Bremsstrahlung in intermediate-energy nucleon reactions within an effective one-boson exchange model

Within a covariant effective one-boson exchange model for the $T$ matrix of $NN$ interactions we present detailed calculations of bremsstrahlung cross sections for proton - proton and proton - neutron reactions at beam energies in the 1 GeV region. Besides pure bremsstrahlung processes we consider photons from $\Delta$ decays and contributions from the $\eta \to \gamma \gamma$ process. At beam energies above 700 MeV the $\Delta$ decay channel dominates the spectra at large photon energies, where the interference between non-resonance processes and the $\Delta$ decay channel becomes also important. Low energy photons stem from pure bremsstrahlung processes. The available experimental data at 730 MeV beam energy is well described. We extrapolate the model down to 280 MeV, where more detailed experimental data exist, and find agreement with angular distributions.Comment: 20 pages with 10 figures, to be published in Nucl. Phys.

Production of ϕ\phi mesons in near-threshold π N\pi\,N and N NN\,N reactions

We analyze the production of $\phi$ mesons in $\pi N$ and $NN$ reactions in the near-threshold region, using throughout the conventional “non-strange” dynamics based on such processes which are allowed by the non-ideal $\omega-\phi$ mixing. We show that the occurrence of the direct $\phi NN$ interaction may show up in different unpolarized and polarization observables in $\pi N\to N\phi$ reactions. We find a strong non-trivial difference between observables in the reactions $pp\to pp\phi$ and $pn\to pn\phi$ caused by the different role of the spin singlet and triplet states in the entrance channel. A series of predictions for the experimental study of this effect is presented