Peripheral Production and Decay of Resonances in High-Energy Meson-Nucleon Collisions

Data on quasi-two-body reactions initiated by high-energy meson-nucleon collisions are analyzed from the viewpoint of the peripheral model. The basic interaction mechanism is assumed to be pseudoscalar and/or vector exchange, and absorptive effects arising from coupling between different channels are taken into account. Excellent agreement is found between the one-pion-exchange model and the production and decay data for the processes ${\pi }^{\pm }p\to {\rho }^{\pm }p$ for incident momenta from ∼2 to 8 GeV/c. A unified analysis of the reactions $K^{\pm }p\to K^{*\pm }p$ at 3 GeV/c, and $K^{+}n\to K^{0}p$ at 2.3 GeV/c, is presented; a single pair of vector coupling constants is able to account for the various angular distributions of production. The theory predicts, and preliminary data confirm, appreciable momentum-transfer dependence of the $K^{*}$ spin-density matrix. Equally satisfactory fits to the data are found for $K^{+}p\to K^0{N}^{*++}$ at 3 GeV/c, $K^{-}p\to {\pi }^{-}{Y}^{*}$ (1385) at 2.24 GeV/c, and ${\pi }^{+}n\to \omega p$ at 3.25 GeV/c. In the latter reaction the absorption model reproduces the large departure of the $\omega$-decay correlations from those characteristic of $\rho$ exchange in the absence of absorption. The model cannot explain why the differential cross section for ${\pi }^{+}p\to {\pi }^0{N}^{*}$ is considerably narrower than for $K^{+}p\to K^0{N}^{*}$. The theoretical momentum-transfer distributions and decay correlations for double resonance production ($\pi p\to \rho N^{*}$, $\mathrm{Kp}\to K^{*}{N}^{*}$) are in general agreement with the data, as are the results on combined decay correlations of $\rho$ and $N^{*}$ in ${\pi }^{+}p\to {\rho }^0{N}^{*}$. But the calculated absolute cross sections are considerably larger than observed, probably because the model fails to include the requirements of unitarity, important when the couplings are large. The determination of vector-meson coupling constants is discussed. Because of fundamental difficulties associated with vector-meson exchange amplitudes at high energies, it is concluded that important refinements of the model are necessary if such coupling constants are to be inferred from the data.