Yu. S. Surovtsev

Multichannel approach to studying scalar resonances (

SummaryTheN-channel formalism (in more detail, 2- and 3-channel) is presented which is based on such general principles, as analyticity and unitarity, and realizes an idea of the consistent account of the nearest (to the considered physical region) singularities on all sheets of the Riemann surface of theS-matrix, thus giving a chance to obtain model-independent information on multichannel resonances from the analysis of data on the coupled processes. The resonance representations by pairs of complex-conjugate clusters of poles and zeros on the Riemann surface and the conception of standard clusters as a model-independent test of the resonance presence are discussed. The role of closed channels in forming resonances and fictitious states is investigated. The method is exemplified with the isoscalars-wave channel of coupled processes ππ→ππ, K

Mesons of the f0 family in processes ππ↦ππ, K¯K up to 2 GeV and the chiral-symmetry breaking

\overline K

ON SCALAR MESONS FROM THE COMBINED ANALYSIS OF MULTI-CHANNEL ππ SCATTERING AND J/ψ DECAYS

, ππ and with analysing ππ scattering up to 1.9 GeV and scalar resonances.

SCALAR AND TENSOR STATES IN PROCESSES WITH PSEUDOSCALAR MESONS

The coupled processes -- the pion-pion scattering and pi pi --> K antiK in the I^GJ^{PC}=0^+0^{++} channel -- are analyzed (both separately and combined) in a model-independent approach based on analyticity and unitarity and using a uniformization procedure. It is shown: 1) a structure of the Riemann surface of the S-matrix for considered coupled processes must be allowed for calculating both amplitudes and resonance parameters, such as the mass and width; 2) the combined analysis of coupled processes is needed as the analysis of only pi-pi channel does not give correct values of resonance parameters even if the Riemann surface structure is included.

Effect of the ηη channel and interference phenomena in the two-pion transitions of charmonia and bottomonia

In a combined analysis of the experimental data on the coupled processes

The interference effects of multi-channel pion-pion scattering contributions to the final states of Ψ- and γ-meson family decays

\pi\pi\to\pi\pi,K\bar{K}

Parameters of scalar resonances from the combined analysis of data on processes

in the channel with

\pi\pi \to K\overline{K}, \eta\eta

I^GJ^{PC}=0^+0^{++}