Structure of the Roper Resonance from Alpha-Proton and Pi-Nucleon Scattering

Existing data on the Roper resonance N*(1440) excitation in hadronic reactions were reanalyzed in a consistent way, which requires the assumption of two P₁₁ structures, a scalar N* resonance and a second order excitation of the Δ resonance. In this way, all data on α-p and π-N scattering are well described. This also yields a consistent description of 2π°-photoproduction, where the second structure is observed only. The fact that the first N* resonance (which is strongly excited in α-p) is not seen with photons, supports the conjecture of a pure scalar N* excitation.