Unstable-particles pair production in MPTapproach in NNLO

We consider pair production and decay of fundamental unstable particles in the framework of a modified perturbation theory treating resonant contributions in the sense of distributions. Outcomes of a numerical simulation up to the NNLO with taking into account universal massless-particles contributions are presented.Comment: 3 pages, 1 figure, Talk given at 14th Lomonosov Conference on Elementary Particle Physics, Moscow, August 19-25, 200

Charge-exchange reactions from the standpoint of the parton model

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.Comment: 18 pages, 8 figures; version to appear in EPJ