Study of baryon and search for dibaryon resonances by the $pp \rightarrow pp\pi^ + \pi^-$ reaction

Abstract

Exclusive measurements of the two-pion production channel $pp \rightarrow pp\pi^ + \pi^-$ have been carried out near threshold at CELSIUS with the PROMICE/WASA detector. They reveal $pp \rightarrow pp^*(1440)\rightarrow pp\sigma \rightarrow pp(\pi^ + \pi^-)_{I = \ell = 0}$ as the dominant process at these energies, however, the data exhibit also significant contributions from $p^*(1440) \rightarrow \Delta \pi \rightarrow p(\pi^ + \pi^-)_{I = \ell = 0}$ . From the observed interference of these Roper decay routes their relative branching ratio is derived. The status on the search for NN-decoupled $NN\pi$ -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.