Gießen 2007 – wissenschaftliches Programm

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HK: Fachverband Physik der Hadronen und Kerne

HK 35: Elektromagnetische und Hadronische Sonden

HK 35.2: Vortrag

Mittwoch, 14. März 2007, 17:15–17:30, A

Excitation of the Roper Resonance in Single- and Double-Pion Production* — Tatiana Skorodko¹, •Heinz Clement¹, Mikhail Bashkanov¹, Evgueni Doroshkevich¹, Murat Kaskulov², Olena Khakimova¹, Florian Kren¹, and Gerhard Wagner¹ for the CELSIUS-WASA collaboration — ¹Physikalisches Institut der Universität Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen — ²Institut für Theoretische Physik, Universität Giessen

The Roper resonance has been a puzzle ever since its detection in π N phase shifts. In most investigations no apparent resonance signatures could be found in the observables. Not only its nature has been a matter of permanent debate, also its resonance parameters show a big scatter in their values.

In the pp→ npπ⁺ reaction measured at CELSIUS-WASA at several energies a pronounced resonance structure at M_nπ⁺ ≈ 1350 MeV with Γ≈ 140 MeV has been found. These numbers agree very favourably with recent SAID π N phase shift results for the Roper pole as well as with the very recent BES results from J/ψ→ NN^*. With the pole position being roughly 100 MeV below the previously believed value of the N^*(1440), also its decay branchings (defined at the pole position) change dramatically. From near-threshold two-pion production, when Roper excitation is the only significant process, we find the decay N^*→ Nσ to be the by far dominant process pointing to a breathing mode nature of the Roper resonance.

*supported by BMBF (06 TU 261), DFG (Europ. Grad. School), COSY-FFE