Measurement of the near-threshold H(${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{+}$${\mathrm{\pi }}^{+}$)n cross section and chiral symmetry

Total cross sections for the H(${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{+}$ ${\mathrm{\pi }}^{+}$)n reaction have been measured at pion kinetic energies of 180, 184, 190 and 200 MeV. The threshold value for the matrix element a(${\mathrm{\pi }}^{+}$ ${\mathrm{\pi }}^{+}$) and the s-wave, isospin-2, ππ scattering length ${\mathit{a}}_2^0$ were determined. The results were found to be in agreement with chiral perturbation theory and inconsistent with the model of dominance by quark loop anomalies.