$\sigma(600)$ and background in $\pi\pi$ scattering

Abstract.

We suggest a simple analytical description of the S-wave isoscalar $\pi\pi$ amplitude, which corresponds to a joint dressing of the bare resonance and background contributions. The amplitude describes well the experimental data on the $\delta^0_0$ phase shift in the energy region below 900 MeV and has two poles in the ${\rm Re}\ s > \ 0$ half-plane. Besides the well-known pole of the $\sigma(600)$-meson with ${\rm Re}\ s \sim m_{\pi}^2$, there exists a more distant pole with $\mathrm{Re} s \tilde 0.6 \mathrm{GeV}^{2}$. Our analysis is interpreted as an indication for the dynamical origin of the $\sigma(600)$ pole, while the second pole should be associated with lowest $q\bar{q}$ state.