Measurements of the reaction ${\pi }^{-}p\to {\pi }^0{\pi }^{0}n$ at incident momenta of 1.715, 1.889, 2.071, 2.265, and $2.460 \frac{\mathrm{GeV}}{c}$ are presented. They show two important contributions to this reaction: (i) production of the 1238-MeV isobar and a recoil pion, and (ii) peripheral production of the dipion system. We explore the consequences of assuming the latter to be due to the reaction ${\pi }^{-}{\pi }^{+}\to {\pi }^0{\pi }^0$. This reaction has the advantage that it cannot take place in an $I=1\mathrm{}$, l=1 state and so should be useful for a study of the $s$-wave $\pi \pi$ interaction. The measured $\pi \pi$ mass spectrum from peripheral production shows no evidence for any of the relatively narrow $s$-wave resonances which have been proposed, but shows a broad peak centered at about 600 and about 400 MeV wide. Some evidence that this peak may be a broad $s$-wave resonance is deduced from a comparison with information about the $s$-wave interaction deduced from the ${\pi }^{-}{\pi }^{+}$ asymmetry in the reaction ${\pi }^{-}p\to {\pi }^{-}{\pi }^{+}n$; conclusions are reached which agree with a number of other experimental results. Against this resonance interpretation we find that a calculation of the peripheral production cross section expected for such a resonance, made by assuming the one-pion-exchange formula with the Ferrari-Selleri form-factor modification, is approximately three times greater than our measured cross section. This may mean that the modification of the one-pion-exchange formula is larger for $s$-wave $\pi \pi$ interaction than it is for $p$ and $d$ waves.

• Received 27 September 1966

DOI:https://doi.org/10.1103/PhysRev.156.1451