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Hadronic Matter is Soft

Ch. Hartnack, H. Oeschler, Joerg Aichelin

nucl-tharXiv:nucl-th/0506087

Abstract

The stiffness of the hadronic equation of state has been extracted from the production rate of K+ mesons in heavy ion collisions around 1 A GeV incident energy. The data are best described with a compressibility coefficient κ around 200 MeV, a value which is usually called ``soft''. This is concluded from a detailed comparison of the results of transport theories with the experimental data using two different procedures: (i) the energy dependence of the ratio of K+ from Au+Au and C+C collisions and (ii) the centrality dependence of the K+ multiplicities. It is demonstrated that input quantities of these transport theories which are not precisely known, like the kaon-nucleon potential, the ΔN N K+ Λ cross section or the life time of the Δ in matter do not modify this conclusion.

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