Measurement of the ${\pi }^{+}{\pi }^{-}\to {K_s}^0{K_s}^0$ Scattering Cross Section

Data from the reaction ${\pi }^{-}p\to n{K_s}^0{K_s}^0$ have been used to determine the cross section for the reaction ${\pi }^{+}{\pi }^{-}\to {K_s}^0{K_s}^0$ by extrapolation to the pion pole. The reaction ${\pi }^{+}{\pi }^{-}\to {K_s}^0{K_s}^0$ is dominated by $S^{*}$ and $f^0$ production. The ${\pi }^{+}{\pi }^{-}\to {K_s}^0{K_s}^0$ cross section is well below the $S$-wave unitarity limit in the $S^{*}$ (threshold) region. We discuss implications for the SU(3) scalar meson nonet and for $\pi \pi$ phase-shift analyses.