Low-energy pion-pion scattering in the pp to ppπ⁺π⁻ and pbar p to pbar pπ⁺π⁻ reactions

We evaluate the contribution of pion-pion rescattering to the $p p \to p p \pi^+ \pi^-$ and $p \bar p \to p \bar p \pi^+ \pi^-$ reactions. We compare our results with the close-to-threshold experimental data. The pion-pion rescattering contribution is found there to be negligible. The predictions for future experiments with PANDA detector at High Energy Storage Ring (HESR) in GSI Darmstadt are presented. It is discussed how to cut off the dominant Roper resonance and double-$\Delta$ excitation mechanisms leading to the $p p \pi^+ \pi^-$ channel in final state. Differential distributions in momentum transfers, transverse momentum, effective two-pions mass, relative azimuthal angle between pions, and pion rapidities are presented.