Seminarium Fizyki Wielkich Energii

According to QCD, strong interactions of a hadron with virtual quark-antiquark pairs in the vacuum are the process responsible for the acquisition of most of hadron's mass from the sum of current quark masses. During the relativistic collision of heavy ions the reverse process should occur, called the partial restoration of chiral symmetry. A hadron in hot and dense nuclear matter should change its basic properties like mass and decay constant with respect to the well known values in vacuum.Kaons produced in heavy ion collisions around threshold for their production in NN collision appear to be a good probe of these effects.First comparisons of experimentally found phase space distributions of kaons to the transport model calculations suggested a clear sensitivity to this effect. Meanwhile the theoretical predictions suggested that the mass change should be not only density-dependent, but also momentum-dependent. In the seminar these comparison will be presented.However, data from collisions around strangeness threshold published recently by HADES and FOPI suggest a much broader and complex landscape. Any extraction of possible changes of K- mass has to account for the downfeed from Phi meson decay. Also, comparisons for K0s and Lambda emitted from Au+Au at 1.2A GeV show that the model description is still not fully consistent.