Neutral-kaon system in dense matter and heavy-ion collisions

Above a critical matter density the propagating modes of the neutral kaon system are essentially eigenstates of strangeness, but below it they are almost complete eigenstates of CP. We estimate the real and imaginary parts of the energies of these modes and their mixing at all densities up to a nuclear matter density of 2×1014 g/cm3. In a heavy-ion collision the strong interactions create eigenstates of strangeness, and these propagate adiabatically until the density has fallen to the critical value, whereupon the system undergoes a sudden transition to (near) eigenstates of CP. We estimate the critical density to be 20 g/cm3, and that this density will be reached about 2×105 fm/c after the end of the collision.