Three-body nature of N() and Δ() resonances from sequential decay chains

• Published in: Physical review letters 2015-03, Vol.114 (9), p.091803-091803, Article 091803
• Main Authors: Thiel, A, Sokhoyan, V, Gutz, E, van Pee, H, Anisovich, A V, Bacelar, J C S, Bantes, B, Bartholomy, O, Bayadilov, D, Beck, R, Beloglazov, Yu, Castelijns, R, Crede, V, Dutz, H, Elsner, D, Ewald, R, Frommberger, F, Fuchs, M, Funke, Ch, Gregor, R, Gridnev, A, Hillert, W, Hoffmeister, Ph, Horn, I, Jaegle, I, Junkersfeld, J, Kalinowsky, H, Kammer, S, Kleber, V, Klein, Frank, Klein, Friedrich, Klempt, E, Kotulla, M, Krusche, B, Lang, M, Löhner, H, Lopatin, I, Lugert, S, Mertens, T, Messchendorp, J G, Metag, V, Metsch, B, Nanova, M, Nikonov, V, Novinski, D, Novotny, R, Ostrick, M, Pant, L, Pfeiffer, M, Piontek, D, Roy, A, Sarantsev, A V, Schmidt, Ch, Schmieden, H, Shende, S, Süle, A, Sumachev, V V, Szczepanek, T, Thoma, U, Trnka, D, Varma, R, Walther, D, Wendel, Ch, Wilson, A
• Format: Article
• Language: English
• Subjects: Decomposition; Formations; Isobars; Nucleons; Parity; Photoproduction; Pions
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.114.091803

The Nπ^{0}π^{0} decays of positive-parity N^{*} and Δ^{*} resonances at about 2 GeV are studied at ELSA by photoproduction of two neutral pions off protons. The data reveal clear evidence for several intermediate resonances: Δ(1232), N(1520)3/2^{-}, and N(1680)5/2^{+}, with spin parities J^{P}=3/2^{+}, 3/2^{-}, and 5/2^{+}. The partial wave analysis (within the Bonn-Gatchina approach) identifies N(1440)1/2^{+} and the N(ππ)_{S wave} (abbreviated as Nσ here) as further isobars and assigns the final states to the formation of nucleon and Δ resonances and to nonresonant contributions. We observe the known Δ(1232)π decays of Δ(1910)1/2^{+}, Δ(1920)3/2^{+}, Δ(1905)5/2^{+}, Δ(1950)7/2^{+}, and of the corresponding spin-parity series in the nucleon sector, N(1880)1/2^{+}, N(1900)3/2^{+}, N(2000)5/2^{+}, and N(1990)7/2^{+}. For the nucleon resonances, these decay modes are reported here for the first time. Further new decay modes proceed via N(1440)1/2^{+}π, N(1520)3/2^{-}π, N(1680)5/2^{+}π, and Nσ. The latter decay modes are observed in the decay of N^{*} resonances and at most weakly in Δ^{*} decays. It is argued that these decay modes provide evidence for a 3-quark nature of N^{*} resonances rather than a quark-diquark structure.