Tübingen 2003 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 17: Elektromagnetische und hadronische Proben II

HK 17.11: Talk

Tuesday, March 18, 2003, 18:30–18:45, B

First Results from the WASA 4π Detector for pp → NNππ and the Quest about the Nature of the Roper Resonance^∗ — •M. Bashkanov, T. Skorodko, H. Clement, E. Dorochkevitch, M. Kaskulov, R. Meier, and G.J. Wagner — Physikalisches Institut der Universität Tübingen

The WASA detector being capable to detect charged and neutral particles in full 4π geometry has reached its production phase at the CELSIUS storage ring in fall 2002. First measurements have been carried out with a proton beam incident on a windowless target of frozen hydrogen pellets. Aside from η production studies first two-pion production data have been taken at T_p = 775 and 900 MeV. First results of these exclusive measurements will be presented for both π⁺π⁻ and π⁰π⁰ channels and compared to the PROMICE/WASA results [1] obtained at lower energies and in a restricted angular range.
The invariant mass spectra and angular distributions partly show strong deviations from phase space. They will be discussed with respect to the excitation of the Roper resonance and its interfering decay routes N^∗→ Nσ → N(ππ)_I=ℓ=0 and N^∗→ Δ π → N(ππ)_I=ℓ=0. Possible scenarios of the nature of Roper and σ resonances will be considered.
[1] W. Brodowski et al., Phys. Rev. Lett. 88, 192301 (2002)
^∗supported by the BMBF (06 TU 987) and DFG (Europ. Graduiertenkolleg)