S-matrix unitarity for overlapping resonances and light vector mesons in e+e- annihilation

Excited states of ρ and ω mesons are studied. These broad overlapping resonances were found in recent years, but their properties have not been established well, and the existence of the lowest mass excitation [ρ'(1250)] is questionable. Analyses are usually based on Breit-Wigner-type formulas, which do not satisfy the unitarity relation for overlapping resonances. Our analysis takes into account an explicitly unitarized multichannel S matrix, and we obtain a good description of e+e--annihilation processes into two- and multipion final states up to about 2 GeV. The method that we developed to deal with broad overlapping resonances with the same quantum numbers can be useful in various problems of particle and nuclear physics