A study of s - wave π π scattering in the reaction πn → ππp at 2.15 GeV/c

We have studied the 2_π⁰ final states in the reaction π⁺d → π⁰π⁰p(p) at 2.15 GeV/c in a 2 million picture exposure of the PPA rapid cycling deuterium bubble chamber. Two tantalum plates were added to the bubble chamber to convert γ rays which were kinematically constrained to a 2π⁰ hypothesis. The 2π⁰ mass spectrum is observed to saturate s-wave unitarity in the ππ mass region between 0.6 and 0.9 GeV/c², clearly favoring the ‘up-down’ or broad resonance solution for s-wave, I = 0, ππ scattering.