Search

The cross-sections of the pd $ \rightarrow$3He $ \eta$ , pd $ \rightarrow$3He $ \pi^{0}_{}$ $ \pi^{0}_{}$ $ \pi^{0}_{}$ and pd $ \rightarrow$3He $ \pi^{+}_{}$ $ \pi^{-}_{}$ $ \pi^{0}_{}$ reactions have been measured at the beam kinetic energies Tp= 1360 MeV and Tp= 1450 MeV using the CELSIUS/WASA detector setup. At both energies, the differential cross-section $\tfrac{{d\sigma }} {{d\Omega }}$ of the $ \eta$ meson in the pd $ \rightarrow$3He $ \eta$ reaction shows a strong forward-backward asymmetry in the CMS. The ratio between the pd $ \rightarrow$3He $ \pi^{+}_{}$ $ \pi^{-}_{}$ $ \pi^{0}_{}$ and pd $ \rightarrow$3He $ \pi^{0}_{}$ $ \pi^{0}_{}$ $ \pi^{0}_{}$ cross-sections has been analysed in terms of isospin amplitudes. The reconstructed invariant-mass distributions of the $ \pi$ $ \pi$ , 3He $\displaystyle \pi$ and 3He2 $ \pi$ systems provide hints on the role of nucleon resonances in the 3 $ \pi$ production process. [ABSTRACT FROM AUTHOR]

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 → pp* (1440) → ppσ → pp(π+ π- as the dominant process at these energies, however, the data exhibit also significant contributions from p*(1440) → Δπ → p(π+π-)I=l=0. From the observed interference of these Roper decay routes their relative branching ratio is derived. The status on the search for NN-decoupled NNπ-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. [ABSTRACT FROM AUTHOR]

In most investigations the Roper resonance is sensed only very indirectly via complex partial-wave analyses. We find indications for its excitation in the invariant nπ+ mass spectrum of the pp → npπ+ reaction at M ≈ 1360 MeV with a width of ≈ 150 MeV . The values fit very favorably to the most recent phase shift results as well as to the observations at BES. In the near-threshold two-pion production pp → ppπ0π0 , where the Roper excitation and its subsequent decays via the routes N * → Δπ → Nππ and N * → Nσ are the only dominant processes, we find its direct decay into the Nσ channel to be the by far dominating decay process --in favor of a monopole excitation of the Roper resonance. [ABSTRACT FROM AUTHOR]

In most investigations the Roper resonance is sensed only very indirectly via complex partial-wave analyses. We find indications for its excitation in the invariant nπ+ mass spectrum of the pp → npπ+ reaction at M ≈ 1360 MeV with a width of ≈ 150 MeV . The values fit very favorably to the most recent phase shift results as well as to the observations at BES. In the near-threshold two-pion production pp → ppπ0π0 , where the Roper excitation and its subsequent decays via the routes N * → Δπ → Nππ and N * → Nσ are the only dominant processes, we find its direct decay into the Nσ channel to be the by far dominating decay process --in favor of a monopole excitation of the Roper resonance. [ABSTRACT FROM AUTHOR]