Baryon-exchange Deck-model contributions to nucleon diffraction dissociation

In a Drell-Deck- model description of high-energy nucleon diffraction dissociation, $aN\to a\left(N\pi \right)$, we study the contributions which the baryon-exchange and direct-baryon-pole Deck graphs make to the production and decay distributions of the low-mass $N\pi$ system. We treat spin effects explicitly. Because the two baryon amplitudes cancel each other to a remarkable degree, their sum has only a small effect (∼20%) on the overall cross section, which is dominated by the pion-exchange Deck amplitude. Nevertheless, the baryon terms have an important influence on the decay angular distributions of the $N\pi$ system, particularly in that region of phase space in which the pion-exchange term is suppressed. They also provide a pronounced increase in the slope of the production-momentum-transfer ($t$) distribution near the $N\pi$ threshold. Both of these results improve the agreement of the unabsorbed Deck model with recent data on $\mathrm{NN}\to N\left(N\pi \right)$ from Fermilab and the CERN ISR. Discrepancies remain in the description of certain correlations between structure in the $t$ distribution and selections on the decay angles. We speculate that this failure suggests the presence of a second non-Deck, perhaps resonant, component in the data and the necessity for a coupled analysis in which final-state interactions are included.