Hypothesis ofM1Dominance in32+-Isobar Production Reactions

Abstract

The hypothesis that the $\rho N\Delta$ and $A_{2}N\Delta$ vertices are predominantly of the magnetic-dipole ($M1\mathrm{}$) type is investigated in detail with reference to the ${\frac{3}{2}}^{+}$-isobar production reactions at high energies. The incorporation of this hypothesis for the Regge exchanges of $\rho$ and $A_2$ mesons is greatly facilitated by our choice of Reggeizing the invariant amplitudes, a choice which avoids spurious parametrizations of the unknown Regge residues and which automatically satisfies all the constraint conditions at the normal thresholds and pseudothresholds. The simple model which assumes only $M1\mathrm{}$ couplings and $\mathrm{SU}\left(3\right)\mathrm{}$ symmetry at the Regge vertices is in satisfactory agreement with the available high-energy data on the differential cross sections and density matrix elements of the reactions ${\pi }^{+}p\to {\pi }^0\left(\eta \right){\Delta }^{++}$, ${\pi }^{-}p\to {\pi }^{-}{\Delta }^{+}$, and $K^{+}p\to K^0{\Delta }^{++}$. The presence of a small $E2\mathrm{}$ coupling at the vector-meson vertex, in addition to the dominant $M1\mathrm{}$ coupling, is shown to provide an improved fit with experiment near the forward direction.