Global description of0−12+→0−12+reactions utilizing the bare Pomeron

Abstract

It is shown that the combination of a "bare Pomeron" with intercept ${\stackrel{^}{\ensuremath{\alpha}}}_{P}(0)=0.85$ in conjunction with a reasonable set of secondary Regge trajectories and a canonical absorption prescription is capable of providing a good global fit to practically all ${0}^{\ensuremath{-}}{\frac{1}{2}}^{+}\ensuremath{\rightarrow}{0}^{\ensuremath{-}}{\frac{1}{2}}^{+}$ meson-nucleon scattering data up to lab momenta of 30 GeV/c. The bare Pomeron with intercept lower than 1 has a large real part which greatly facilitates the description of the data. At higher energies, "renormalization" effects can be expected to be important as inelastic diffraction events, and these lead to a renormalized Pomeron intercept very close to or equal to one. The value ${\stackrel{^}{\ensuremath{\alpha}}}_{P}(0)=0.85$ used throughout this intermediate-energy fit is in agreement with current inclusive triple-Regge data and maximum-rapidity-gap distributions. It is also in agreement with certain strong-coupling ABFST (Amati-Bertocchi-Fubini-Stanghellini-Tonin) multiperipheral model calculations. For secondary effects, we have used a family of vector Regge trajectories ($\ensuremath{\rho},\ensuremath{\omega},{K}^{*}$) with a degenerate intercept of about 0.45, and tensor trajectories (${A}_{2},{K}^{**}$) with an intercept of about 0.25. A second vacuum pole emerges with intercept close to 0. The ${p}^{\ensuremath{'}} (f)$ trajectory, not included here, can perhaps be expected to appear in conjunction with the renormalization of the Pomeron. Although no wrong-signature nonsense zeros are included in the parametrization, the $\ensuremath{\rho}\ensuremath{-}{A}_{2}$ and ${K}^{*}\ensuremath{-}{K}^{**}$ pole couplings are nevertheless very nearly exchange degenerate. SU(3) is used to relate most of the other couplings. The (pole + cut) helicity-flip $\ensuremath{\rho}\ensuremath{-}{A}_{2}$ and ${K}^{*}\ensuremath{-}{K}^{**}$ amplitudes also show considerable exchange-degenerate characteristics. We have used a standard absorption prescription to calculate the second-order bare Pomeron $(\stackrel{^}{P})\ensuremath{\bigotimes}$ Reggeon cuts and $\stackrel{^}{P}\ensuremath{\bigotimes}\stackrel{^}{P}$ cuts. An unusual result emerges---the "enhancement" ${\ensuremath{\lambda}}_{i}$ factors for all cuts are less than one. This indicates the presence of higher-order cuts which thus dominate over inelastic intermediate-state production in this approach. The data used in this fit are a representative selection of ${0}^{\ensuremath{-}}{\frac{1}{2}}^{+}\ensuremath{\rightarrow}{0}^{\ensuremath{-}}{\frac{1}{2}}^{+}$ data (including $\ensuremath{\pi}N$ amplitude analysis, hypercharge-exchange differential cross sections and polarizations; ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}p$ and ${K}^{\ifmmode\pm\else\textpm\fi{}}p$ total and differential cross sections, polarizations, and $t=0$ real-to-imaginary ratios; and $\ensuremath{\pi}N$ and $\mathrm{KN}$ charge-exchange differential cross sections and polarizations) up to ${p}_{\mathrm{lab}}=30$ GeV/c and $|t|=1.5$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$.