Measurement of the in-medium K0 inclusive cross section in pi(-) -induced reactions at 1.15 GeV/c

Strong Absorption of Hadrons with Hidden and Open Strangeness in Nuclear Matter

We present the first observation of K^{-} and ϕ absorption within nuclear matter by means of π^{-}-induced reactions on C and W targets at an incident beam momentum of 1.7  GeV/c studied with HADES at SIS18/GSI. The double ratio (K^{-}/K^{+})_{W}/(K^{-}/K^{+})_{C} is found to be 0.319±0.009(stat)_{-0.012}^{+0.014}(syst) indicating a larger absorption of K^{-} in heavier targets as compared to lighter ones. The measured ϕ/K^{-} ratios in π^{-}+C and π^{-}+W reactions within the HADES acceptance are found to be equal to 0.55±0.04(stat)_{-0.07}^{+0.06}(syst) and to 0.63±0.06(stat)_{-0.11}^{+0.11}(syst), respectively. The similar ratios measured in the two different reactions demonstrate for the first time experimentally that the dynamics of the ϕ meson in nuclear medium is strongly coupled to the K^{-} dynamics. The large difference in the ϕ production off C and W nuclei is discussed in terms of a strong ϕN in-medium coupling. These results are relevant for the description of heavy-ion collisions and the structure of neutron stars.

Inclusive K+ production in π− + A collisions at 1.7 GeV/c

The production and properties of K+ in nuclear reactions π− + A (A = C; W) at an incident beam momentum of 1.7 GeV/c has been studied with the HADES setup at SIS18/GSI. Phase space distributions of kaons produced off heavy and light nuclei can be studied to extract information about the KN potential. We present the analysis method, normalization procedure and first results on the ratio of inclusive (K+) cross-sections in π−-induced reactions on W and C targets in comparison to existing measurement by FOPI and ANKE.

Kaon and Phi Production in Pion-Nucleus Reactions at 1.7 GeV/c

The production and properties of K+, K− and ϕ in nuclear reactions π− + A (A = C,W) at a beam momentum of 1:7 GeV/c has been studied with the HADES setup at SIS18/GSI. Of particular interest is the K− absorption in nuclear matter which should be driven by strangeness exchange processes on one (K−N → Yπ) or more nucleons (K−NN → YNπ). In this context, also the ϕ has to be taken into account, since ϕ decays into K+K− pairs may substantially affect the measured K− abundance. A solid reference is needed to evaluate the K− absorption with in the nucleus and in this work we discuss the determination of this reference. A double ratio of K−=K+(W)=K−=K+(C) is measured within the acceptance and compared to the reference.

Strangeness at high μB: Recent data from FOPI and HADES

Strangeness production in heavy-ion reactions at incident energies at or below the threshold in NN collisions gives access to the characteristics of bulk nuclear matter and the properties of strange particles inside the hot and dense nuclear medium, like potentials and interaction cross sections. At these energies strangeness is produced in multi-step processes potentially via excitation of intermediate heavy resonances. The amount of experimental data on strangeness production at these energies has increased substantially during the last years due to the FOPI and the HADES experiments at SIS18 at GSI. Experimental data on K+ and K0 production support the assumption that particles with an s quark feel a moderate repulsive potential in the nuclear medium. The situation is not that clear in the case of K-. Here, spectra and flow of K- mesons is influenced by the contribution of ø mesons which are decaying into K+K- pairs with a branching ratio of 48.9 %. Depending on incident energy upto 30 % of all K- mesons measured in heavyion collisions are originating from ø-decays. Strangeness production yields - except the yield of Ξ- are described by thermal hadronisation models. Experimental data not only measured for heavy-ion collisions but also in proton induced reactions are described with sets of temperature T and baryon chemical potential μb which are close to a universal freeze-out curve which is fitting also experimental data obtained at lower baryon chemical potential. Despite the good description of most particle production yields, the question how this is achieved is still not settled and should be the focus of further investigations.