The associated strangeness dissociation at threshold has been studied at the COSY-11 facility measuring the hyperon- and the K+K- meson pair production.
Measurements of the near threshold Lambda and Sigma0 via the pp->pK+Lambda/Sigma0 reaction [1] at COSY-11 have shown that the Lambda/Sigma0 cross section ratio exceeds the value at high excess energies (Q >= 300 MeV [2]) by an order of magnitude. For a better understanding additional data have been taken between 13 MeV and 60 MeV excess energy.
The near threshold production of the charged kaon-antikaon pair is related to the discussion about the nature of the scalar states in the 1 GeV/c² mass range, i.e. the f0(980) and a0(980) [3]. The interpretation as a K anti-K molecule is strongly dependent on the K-anti-K interaction which can be studied via the production channel. A first total cross section value on the reaction pp->ppK+K- at an excess energy of 17 MeV [4] i.e. below the phi production threshold was measured.
[1] S.Sewerin et al., Phys. Rev. Lett. 83 (1999) 682.
[2] A.Baldini et al., "Total Cross-Sections for
Reactions of High-Energy Particles",
(Landolt-Börnstein, New Series I/12, Springer, Berlin
1988).
[3] O.Krehl, R.Rapp, J.Speth, Phys. Lett. B390 (1997) 23.
[4] C.Quentmeier et al., Phys. Lett. B515 (2001) 276.
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Eur.Phys.Jou. A
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