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HK: Physik der Hadronen und Kerne

HK 38: Electromagnetic and Hadronic Probes VI

HK 38.4: Vortrag

Donnerstag, 11. März 2004, 14:45–15:00, B

Two-Pion Production at CELSIUS-WASA and the Quest for the Nature of σ Meson and Roper Resonance^∗ — •T. Skorodko, M. Bashkanov, H. Clement, E. Doroshkevich, M. Kaskulov, R. Meier, and G.J. Wagner — Physikalisches Institut, Universität Tübingen

The two-pion production in proton-proton collisions has been measured at CELSIUS in the energy range T_p = 775 - 1360 MeV using the WASA 4π detector with hydrogen pellet target. The WASA detector containing magnetic field, tracking detectors and calorimeter, allows the detection of both charged and neutral particles. The channels ppπ⁺π⁻, ppπ⁰π⁰ and dπ⁺π⁰ have been measured exclusively with 4 overconstraints. Our first exclusive ppπ⁺π⁻ data taken at PROMICE/WASA near threshold have been shown [1] to be in agreement with the process proceeding via the Roper resonance as predicted by calculations of the Valencia group [2]. Alternatively, the data are equally well described by ππ rescattering leading to a dynamic formation of the σ meson. With increasing incident energies the agreement of the Valencia prediction with the new data in ppπ⁺π⁻ and ppπ⁰π⁰ channels gets worse and finally at variance for T_p > 1 GeV. Rather the data in these channels get consistent with the formation of a (ΔΔ)_0⁺ configuration at the highest energies. In the dπ⁺π⁰ channel the data show the onset of ρ-production.

[1] Brodowski et al. PRL 88 192301 (2002); PRC 67 052202 (2003)

[2] L. Alvarez-Ruso et al., Nucl. Phys. A633, 519 (1998) ^∗supported by the BMBF (06 TU 201), DFG (Europ. Graduiertenkolleg) and Landesforschungsschwerpunkt (Quasiteilchen)