Aspects of particle production in isospin-asymmetric matter

The production/absorption rate of particles in compressed and heated asymmetric matter is studied using a Relativistic Mean Field (RMF) transport model with an isospin-dependent collision term. Just from energy conservation in the elementary production/absorption processes we expect to see a strong dependence of the yields on the basic Lorentz structure of the isovector effective interaction, due to isospin effects on the scalar and vector self-energies of the hadrons. This will be particularly evident for the ratio of the rates of particles produced with different charges: results are shown for pi(+)/pi(-), K+/K-0 yields. In order to simplify the analysis we perform RMF cascade simulations in a box with periodic boundary conditions. In this way we can better pin down all such fine relativistic effects in particle production, that could likely show up even in realistic heavy ion collisions. In fact, the box properties are tuned in order to reproduce the heated dense matter formed during a nucleus-nucleus collision in the few A GeV beam energy region. In particular, K+.0 production is expected to be directly related to the high density behaviour of the symmetry energy, since kaons are produced very early during the high density stage of the collision and their mean free path is rather large. We show that the K+/K-0 ratio reflects important isospin contributions on the production rates just because of the large sensitivity around the threshold. The results are very promising for the possibility of a direct link between particle production data in exotic Heavy Ion Collisions (HIC) and the isospin-dependent part of the Equation of State (EoS) at high baryon densities. (c) 2005 Elsevier B.V. All rights reserved.