Available online at www.sciencedirect.com Nuclear Physics A 914 (2013) 392–395 www.elsevier.com/locate/nuclphysa What heavy ion can teach us about strange particles and what strange particles can teach us about heavy ions? C. Hartnack a , H. Oeschler b , Y. Leifels c , E.L. Bratkovskaya d , J. Aichelin d,∗ a SUBATECH, University of Nantes, IN2P3/CNRS, Ecole des Mines de Nantes, 4 rue Alfred Kastler, F-44072 Nantes, Cedex 03, France b Institut für Kernphysik, Darmstadt, 64289 Darmstadt, Germany c GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany d Institute for Theoretical Physics and Frankfurt Institut for Advanced Studies, Frankfurt University, 60438 Frankfurt-am-Main, Germany Received 11 December 2012; received in revised form 16 May 2013; accepted 17 May 2013 Available online 22 May 2013 Abstract We show that heavy ion collisions can reveal properties of K + in matter, here demonstrated for the KN optical potential, and that at the same time the K + yield is sensitive to nuclear matter properties, here demonstrated for the hadronic equation of state. © 2013 Elsevier B.V. All rights reserved. Keywords: Kaons in matter; Heavy ion collisions Theory predicts that hadronic matter at finite temperatures and densities has a rich structure but even the simple question “How much energy is needed to compress hadronic matter?” has, after 70 years of nuclear physics, not found a definite answer yet, despite of the importance of the answer not only for a fundamental understanding of hadronic matter but also for the understand- ing of many astrophysical observations. This search has been dubbed ‘Quest for the hadronic equation of state’ (EoS). The most simple approach to E(ρ)/A, the energy/nucleon of cold mat- ter as a function of the density, is a three parameter approach * Invited speaker. E-mail address: aichelin@subatech.in2p3.fr (J. Aichelin). 0375-9474/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nuclphysa.2013.05.010