Experimental study of the near thresholdπ+p→π+π+ncross section and chiral symmetry

Total cross-section measurements of the ${\pi }^{+}p\to {\pi }^{+}{\pi }^{+}n$ reaction at pion kinetic energies of 180, 184, 190, and 200 MeV are reported. The threshold value for the amplitude $a\left({\pi }^{+}{\pi }^{+}\right)$ as well as the $s$-wave, isospin 2, $\pi \pi$ scattering length $a_2^0$ were determined. The results were found to be in agreement with chiral perturbation theory and inconsistent with the calculations of Jacob and Scadron and the model of dominance by quark loop anomalies.