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

Non-coherent contributions in charge-exchange reactions and η\eta--η′\eta' mixing

We analyse $K^- p \to (\eta, \eta',\pi^0) \Lambda$ on the basis of the fit of data in a wide region of energies, and $\pi^- p \to (\eta, \eta') n$ at the energies of GAMS-4$\pi$. We show that disagreements between the data and the predictions of Regge theory may be explained by the mode change of summation of intermediate contributions at increasing energy, from coherent to non-coherent. A method of experimental measurement of the non-coherent contributions is proposed. On the basis of available data on the charge-exchange reactions the $\eta$--$\eta'$ mixing is estimated.Comment: 18 pages, 4 figures; version to appear in EPJ