The $p\overrightarrow{p}\mathrm{pp}{\pi }^{+}{\pi }^{-}$ reaction studied in the low-energy tail of the Roper resonance

Exclusive measurements of the $p\overrightarrow{p}\mathrm{pp}{\pi }^{+}{\pi }^{-}$ reaction have been carried out at $T_p=775\mathrm{}\mathrm{MeV}$ at CELSIUS using the PROMICE/WASA setup. Together with data obtained at lower energy, they point to a dominance of the Roper excitation in this process. From the observed interference of its decay routes $N^{*}\to N\sigma$ and $N^{*}\to \Delta \overrightarrow{\pi }N\sigma ,$ their energy-dependent relative branching ratio is determined.