Mechanism of Pion Production in $alpha$p Scattering at 1 GeV/nucleon
  The one-pion and two-pion production in the p(alpha, alpha prime)X reaction at an energy of E{alpha} = 4.2 GeV has been studied by simultaneous registration of the scattered alpha particles and the secondary pion or proton. The obtained results demonstrate that the inelastic alpha-particle scattering on the proton at the energy of the experiment proceeds either through excitation and decay of Delta resonance in the projectile or through excitation in the target proton of the Roper resonance, which decays mainly on a nucleon and a pion or a nucleon and a sigma meson - system of two pions in the isospin I = 0, S-wave. 
G. D. Alkhazov, A. V. Kravtsov, A. N. Prokofiev, I. B.Smirnov
nucl-ex hep-ex