On the production mechanism of Sigma-hypernuclear systems in A(K-,pi+-) reactions

It is shown that the new data on the excitation energy Eex spectrum of the residual nuclear system in the Sigma-hypernuclear region in the reactions (K-,pi+-) on Be-9 and in the reaction (K-,pi+) on He-4 and C-12 can be described without the supposition on the existence of excited Sigma-hypernuclear states. The basis is formed by a simultaneous consideration of the quasi-free Sigma production and Sigma-nuclear rescattering (elastic and with Sigma -> Lambda conversion) with account of interference of the respective amplitudes. For final decision of the question about the nature of the irregularities in Eex spectrum, it is proposed to study the picture corresponding to the so-called moving complex singularity of the triangle graph with Sigma rescattering: the position and the width of the peak in Eex distribution must appreciably change with momentum transferred from the initial kaon to the final pion.