Summary of π-π scattering experiments

The ππ scattering amplitude at threshold is fully determined by the chiral symmetry breaking part of the strong interaction, and, thus, directly constrains the form of the low energy effective lagrangians. Current status of the study of the low energy ππ interaction is discussed, particularly the recent results on reactions πN → ππN near threshold. Present levels of experimental uncertainties and limitations inherent to the available analysis methods leave ample room for improvements in the determination of the s-wave ππ scattering lengths. Experimental improvements are expected from new measurements of Ke4 decays and from attempts to study π+ π- atoms while further theoretical work is required in order to make full use of the extensive near-threshold πN → ππN data that has recently become available. (orig.)