https://doi.org/10.1140/epja/i2008-10569-6
Regular Article - Experimental Physics
Excitation of the Roper resonance in single- and double-pion production in nucleon-nucleon collisions⋆
1
Physikalisches Institut der Universität Tübingen, Auf der Morgenstelle 14, D-72076, Tübingen, Germany
2
Joint Institute for Nuclear Research, Dubna, Russia
3
The Svedberg Laboratory, Uppsala, Sweden
4
Uppsala University, Uppsala, Sweden
5
Hamburg University, Hamburg, Germany
6
Budker Institute of Nuclear Physics, Novosibirsk, Russia
7
Institute of Theoretical and Experimental Physics, Moscow, Russia
8
Soltan Institute of Nuclear Studies, Warsaw, Poland
9
Forschungszentrum Jülich, Germany
10
High Energy Accelerator Research Organization, Tsukuba, Japan
11
Soltan Institute of Nuclear Studies, Lodz, Poland
* e-mail: clement@pit.physik.uni-tuebingen.de
Received:
18
January
2008
Accepted:
21
January
2008
Published online:
9
April
2008
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.
PACS: 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.) – / 14.20.Gk Baryon resonances with S = 0 –
© Società Italiana di Fisica and Springer-Verlag, 2008