Study of baryon and search for dibaryon resonances by the pp → ppπ⁺π⁻ reaction

Abstract

Exclusive measurements of the two-pion production channel pp → ppπ⁺π⁻ have been carried out near threshold at CELSIUS with the PROMICE/WASA detector. They reveal $pp \to pp*\left( {1440} \right) \to pp\sigma \to pp\left( {{\pi ^ + }{\pi ^ - }} \right)I = \ell = 0$ as the dominant process at these energies, however, the data exhibit also significant contributions from ${p^*}\left( {1440} \right) \to \Delta \pi \to p\left( {{\pi ^ + }{\pi ^ - }} \right)I = \ell = 0$ ${p^*}\left( {1440} \right) \to \Delta \pi \to p\left( {{\pi ^ + }{\pi ^ - }} \right)I = \ell = 0$ From the observed interference of these Roper decay routes their relative branching ratio is derived. The status on the search for N N-decoupled N N π-resonances is reviewed with regard to recent experimental searches in the pionic double charge exchange in nuclei, the two-pion production in nucleon-nucleon collisions, the photo pion-production on the deuteron and the electro pion-production in nuclei.