Berlin 2005 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 9: Elektromagnetische und Hadronische Proben
HK 9.1: Gruppenbericht
Freitag, 4. März 2005, 16:30–17:00, TU MA004
Threshold production of open strangeness at COSY-11 — •Peter Winter — Institut für Kernphysik, Forschungszentrum Jülich
Strangeness production in proton-proton collisions enables to study not only nucleon-hyperon but also the KN and KK interaction. The COSY-11 detection system is perfectly suited to investigate such reactions in the near threshold energy region. Exclusive data on hyperon production and open strangeness (pp→ ppK+K−) have been collected. The data in the pp→ pK+Λ/Σ0 reactions revealed a cross section ratio R=σtot(Λ)/σtot(Σ0)≈28 exceeding by an order of magnitude that at high energies. Different models within the framework of one-boson exchange cannot well reproduce this strong rise towards low excess energies Q. Additional information in other isospin channels will impose further constraints to theoretical descriptions and help to clarify the dominant reaction mechanisms. For this purpose, the COSY-11 collaboration gathered data in the channel pp→ nK+Σ+ at Q= 13 and 60 MeV. Besides the hyperon sector, exclusive data on the pp→ ppK+K− reaction have been taken at excess energies of Q=10 and 28 MeV where final state interactions (FSI) of the outgoing particles are pronounced. A strong enhancement of the total cross section close to the threshold compared to a pure phase space expectation is supported by the new data sets. Since the strong pp-FSI is not sufficient to explain this effect, it remains an open question if the rise origins e.g. from the K−p system which should be dominated by the Λ(1405), a K+K− interaction or effects from the 4-body final state. This work is supported by FZ-Jülich and DAAD.