Charge-exchange reactions from the standpoint of the parton model

Abstract

Using simple arguments, we show that charge-exchange reactions at high energies go through the hard scattering of fast quarks. On this basis we describe $\pi^- p \to M^0 n$ and $K^- p \to M^0 \Lambda$, $M^0 =\pi^0, \eta, \eta'$, in a combined approach which defines hard contributions in the parton model and soft ones in Regge phenomenology. The disappearance of a dip according to recent GAMS-4$\pi$ data in the differential cross-section $K^- p \to \eta\Lambda$ at $|t| \approx$ 0.4--0.5 (GeV$\!$/c)$^2$ at transition to relatively high momenta, is explained as a manifestation of a mode change of summation of hard contributions from coherent to incoherent. Other manifestations of the mentioned mode change are discussed. Constraints on the $\eta$--$\eta'$ mixing and gluonium admixture in $\eta'$ are obtained.