Investigation of thep¯dπ+π−Final State inp¯dCoherent Production at5.5GeVc

From 150 000 photographs taken with the 30-in. ANL bubble chamber, we obtained a sample of $\overline{p}d\to \overline{p}d{\pi }^{+}{\pi }^{-}$ events yielding a cross section of 0.22±0.02 mb. The reaction is dominated by ${\overline{\Delta }}^{--}\mathrm{}\left(1236\right)\mathrm{}$ production. A low-mass enhancement in the $d{\pi }^{+}$ mass spectrum appears at $2.2\frac{\mathrm{GeV}}{c^2}$. This bump is interpreted as being due to a final-state interaction, treated as elastic scattering. We used the first-order impulse approximation and $\pi N$ phase shifts which give a satisfactory description of the $\pi d$ elastic scattering data at low energy. A good description of the $d{\pi }^{+}$ mass spectrum is obtained. A peripheral model with a Reggeized $\pi$ exchange which scatters off the deuteron was also considered. Using this model and peripheral phase space, a simultaneous fit on the $d{\pi }^{+}$ and $\overline{p}{\pi }^{+}{\pi }^{-}$ mass distributions was made successfully. The angular distribution of the outgoing deuteron in the ${\pi }^{+}d$ c.m. frame is also well described.