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ISSN - 14346001, EISSN - 1434601X, European Physical Journal A, 2008, vol. 35, p. 317-319

Excitation of the Roper resonance in single- and double-pion production in nucleon-nucleon collisions

Skorodko T., Bashkanov M., Bogoslawsky D., Calen H., Cappellaro F., Clement H., Demiroers L., Doroshkevich E., Duniec D., Ekström C., Franssen K., Gustafsson L., Höistad B., Ivanov G., Jacewicz M., Jiganov E., Johansson T., Khakimova O., Kaskulov M., Keleta S., Koch I., Kren F., Kullander S., Kupść A., Kuznetsov A., Marciniewski P., Meier R., Morosov B., Pauly C., Petterson H., Petukhov Y., Povtorejko A., Schönning K., Scobel W., Shwartz B., Sopov V., Stepeniak J., Thörngren-Engblom P., Tikhomirov V., Wagner G. J., Wolke M., Yamamoto A., Zabierowski J., Złomanczuk J.

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 → ppπ 0π0 , 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. © 2008 Società Italiana di Fisica and Springer-Verlag.