FOPI

Strange mesons are the rare probes of the nucleus-nucleus collisions investigated by the FOPI collaboration at the beam kinetic energy range of 1-2A GeV. This energy falls below ($K^-$, $\phi$(1020) ) or near ($K^+$, $K^0$) thresholds in the free nucleon-nucleon collision, therefore a considerable contribution to the production of these particles is expected to proceed via the secondary channels, involving mesons ($\pi$, $\rho$) and/or intermediate resonances ($\Delta$, $N^$, $\Sigma^$, $\Lambda^$) [1,2]. A particularly interesting case is the $K^-$ meson. Its production in medium is predicted to proceed via the creation of the $\Sigma^$(1385) resonance [3]. However, $K^-$ is also produced in vacuum from the decays of $\phi$ mesons. Both these sources have been investigated by the FOPI Collaboration [4-6]. Strange mesons propagate through the hot and dense collision zone, where their properties like effective mass, and production cross section are modified [3]. These modifications are also studied by the FOPI collaboration in AA and $\pi$A systems by means of comparing the flow observables and ratios of kinematic distributions to the predictions of transport calculations [7,8,9]. In this talk I will present the overview of the abovementioned findings.

[1] C. Fuchs et al., Prog. Part. Nucl. Phys. 56, 1 (2006) [2] H.W. Barz et al., Nucl. Phys A 705, 223 (2002) [3] M.F.M. Lutz, PPNP 53, 125 (2004) [4] X. Lopez et al., Phys. Rev. C 76, 055203(R) (2007) [5] A. Mangiarotti et al., Nucl. Phys. A 714, 89 (2003) [6] P. Gasik, K. Wiśniewski, Acta Phys. Pol. B, 39, 355 (2008) [7] K. Wiśniewski et al., Eur. Phys. J. A 9, 515 (2000) [8] P. Crochet et al., Phys. lett. B 486, 6 (2000) [9] M.L. Benabderrahmane et al., Phys. Rev. Lett. 102, 182501 (2009)