Two-pion production in alpha p scattering at 1-GeV/nucleon in the energy region of the Roper resonance excitation

Semiexclusive measurements of the two-pion-production $p(\ensuremath{\alpha},{\ensuremath{\alpha}}^{'})p\ensuremath{\pi}\ensuremath{\pi}$ reaction have been carried out at an energy of ${E}_{\ensuremath{\alpha}}=4.2$ GeV at the Saturne-II (Saclay) accelerator with the SPES4-\ensuremath{\pi} installation. This reaction was investigated by simultaneous registration of the scattered \ensuremath{\alpha} particle and the secondary proton. The obtained results show that the two-pion production in inelastic \ensuremath{\alpha}-particle scattering on the proton at the energy of the experiment proceeds mainly through excitation in the target proton of the Roper resonance and its decay with emission of two pions in the isospin $I=0,S$-wave state.