Results onπ+π−→π0π0cross section from peripheral dipion production in the reactionπ−p→π0π0nat 2.01 GeV/c

We report results on ${\pi }^{+}{\pi }^{-}\to {\pi }^0{\pi }^0$ total and differential cross sections from threshold to 1.1-GeV $\pi \pi$ mass. These results have been obtained from a high-statistics experiment studying the reaction ${\pi }^{-}p\to {\pi }^0{\pi }^{0}n$ at 2.01 GeV/c incident ${\pi }^{-}$ momentum with the Chew-Low extrapolation method. The ${\pi }^0$'s have been detected and their momenta analyzed in a large-gap cylindrical spark chamber placed in a magnetic field. The results show three salient features: (i) A large $I=0\mathrm{}$ production with ${\sigma }_{\mathrm{tot}}({\pi }^{+}{\pi }^{-}\to {\pi }^0{\pi }^0)$ approaching the $S$-wave unitarity limit in the 550-750-MeV $\pi \pi$ mass region, without any narrow structure. (ii) A slow fall of ${\sigma }_{\mathrm{tot}}({\pi }^{+}{\pi }^{-}\to {\pi }^0{\pi }^0)$ in the region of 750-950-MeV $\pi \pi$ mass. This feature is not predicted by the "down" solution for the $I=0\mathrm{}$ $S$-wave $\pi \pi$ phase shift which has been reported recently. (iii) The presence of $D$-wave effects above 850 MeV as indicated by our extrapolated angular distributions.