D. Krupa

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

SCALAR AND TENSOR STATES IN PROCESSES WITH PSEUDOSCALAR MESONS

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

Physical meaning of the phase of high energy elastic scattering amplitude

On the basis of a simultaneous description of the isoscalar s-wave channel of the

ON NATURE OF SCALAR AND TENSOR MESONS FROM THE ANALYSIS OF PROCESSES ππ → ππ, KK, ηη

\pi\pi

SCALAR AND TENSOR MESONS FROM THE COMBINED ANALYSIS OF THE PROCESSES ππ→ππ,

scattering (from the threshold up to 1.9 GeV) and of the

K\overline{K}

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

, ηη

process (from the threshold to