Strangeness production near threshold in pp-collisions

P.Winter for the COSY-11-Collaboration
Institut für Kernphysik, Forschungszentrum Jülich, 52425 Jülich

Motivated by the ongoing discussion concerning the nature of the scalar resonances f0(980) and a0(980), the COSY-11 [1] collaboration has taken exclusive data on the pp->ppK+K- reaction near the production threshold. A first total cross section sigma = 1.80 ± 0.27 +0.28-0.35 for the excess energy Q = 17 MeV has been determined including statistical and systematical errors [2].

In contrary to the eta, omega and eta' production, the cross section values obtained at COSY-11 [2] and DISTO [3] are in good agreement with one-meson exchange calculations neglecting final state interaction (FSI) effects. The absence of the FSI is not yet understood an d might be explained by either a compensation of the strong pp interaction through a pK- FSI effect or due to an additional degree of freedom caused by the four-body final state. In the latter case, strong FSI effects can be expected at Q-values very close to the K+K- production threshold [4]. Therefore, data at the excess energies Q = 10 and 17 MeV have been taken at COSY-11 and the status of the current analysis will be presented and discussed.

[1] S.Brauksiepe et al., Nucl. Instr. & Meth. A 376 (1996) 397.
[2] C.Quentmeier et al., Phys. Lett. B 515 (2001) 276.
[3] F.Balestra et al., Phys. Rev. C 63 (2001) 024004.
[4] A.Sibirtsev, Publ. of Research Centre Juelich: Matter and Materials 11 (2002) 239.