Double Pion Production without Annihilation in Antiproton-Proton Interactions at 2.7 BeV/c

A study was made of the reaction $\overline{p}p\to \overline{p}p{\pi }^{+}{\pi }^{-}$ at 2.7 BeV/c. The total cross section for this reaction was determined to be 1.93±0.16 mb. The data were found to be consistent with 100% $N^{*}{\overline{N}}^{*}$ formation, where $N^{*}$ is the 1238-MeV pion-nucleon resonance with $T=T_Z=J=\frac{3}{2}$. It was observed that the $N^{*}$ production is highly peripheral; specifically, 50% of the ${\overline{N}}^{*}\text{'}\mathrm{s}$ are formed with ${cos\theta }_p>0.8\mathrm{}$, where ${\theta }_p$ is the angle between the outgoing ${\overline{N}}^{*}$ and incoming $\overline{p}$ momenta in the over-all center-of-mass system. A comparison of the data with predictions of the form-factor and absorption one-pion-exchange models was made.