Hadronic matter is soft.
The stiffness of the hadronic equation of state has been extracted from the production rate of K+ mesons in heavy-ion collisions around 1 AGeV incident energy. The data are best described with a compression modulus K 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, such as the kaon-nucleon potential, the deltaN --> NK+lambda cross section, or the lifetime of the delta in matter, do not modify this conclusion.
SUBATECH, Laboratoire de Physique Subatomique et des Technologies Associées, University of Nantes-IN2P3/CNRS-Ecole des Mines de Nantes, 4 rue Alfred Kastler, F-44072 Nantes CEDEX 03, France.
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Hartnack
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Oeschler
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Aichelin