"Recoil Effects" in a Model of Higher Baryon Couplings. I. Photoproduction

Abstract

A recently proposed model (MM) of higher baryon couplings for $P$ and $V$ mesons is reformulated by reviewing the fuller possibilities of the "recoil term" in the primitive quark-meson interaction. While this introduces no basic change in the $P$-meson coupling structures, it yields an entirely new ($L-1\mathrm{}$)-wave coupling of $V$ mesons to $J=L+\frac{1}{2}$ baryons, which is capable of generating helicity-flip amplitudes. The advantage of this new coupling structure over the earlier one is demonstrated through the excellent reproduction of (i) the $E1\mathrm{}$ angular distribution in $Y^{*}\to \Lambda \gamma$ decay and (ii) the appreciable magnitudes as well as energy variations of the asymmetry parameter $\Sigma \left(\theta \right)$ in pion photoproduction. In addition to a comparison of the two coupling structures (old and new), the present paper is also designed to study the role of still another parametric structure for the form factor - one which exhibits better convergence properties at higher energies than those discussed in MM. The additional processes studied in this connection are (i) $\eta$ and $X_0$ photoproduction at intermediate energies (> 2 GeV), (ii) polarization of the recoil proton in $\eta$ and $\pi$ photoproduction, and (iii) ${\pi }^0$ photoproduction at high energies (∼ 6 GeV), in accordance with our earlier scheme of $s$-channel resonances. In connection with $\eta$ photoproduction the roles of some pertinent $I=\frac{1}{2}$ resonances such as $S_{11}$, $P_{11}$, and $G_{17}$ are discussed, especially in relation to supermultiplet assignments.