Effect of the nuclear compressibility coefficient on the expansion of compressed nuclear matter

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Abstract
On the basis of a conventional nonrelativistic fluid-dynamics model, we study the expansion of spherically symmetric nuclear matter that is initially compressed and excited in head-on collisions of equal targets and projectiles at a laboratory bombarding energy per nucleon of 250 MeV. We use a new functional form for the nuclear equation of state which has the property that the speed of sound approaches the speed of light in the limit of infinite compression. For various values of the nuclear compressibility coefficient, the fluid-dynamical equations of motion are solved until the matter expands to a freezeout density at which fluid dynamics ceases to be valid. At this point the remaining thermal energy is superimposed in terms of a Maxwell-Boltzmann distribution with appropriate nuclear temperature. For nonzero values of the compressibility coefficient ranging form 100 to 400 MeV, the energy distribution at the freezeout density of the expanding matter depends slightly upon the compressibility coefficient. However, the final-energy distribution after thermal folding is independent of the compressibility coefficient to within graphical accuracy. For zero compressibility coefficient, which corresponds to the expansion of a perfect gas, the energy distribution is significantly different form that for nonzero compressibility coefficient at the freezeout point, and is slightly different from that for nonzero compressibility coefficient after thermal folding. For both zero and nonzero values of the compressibility coefficient, the final energy distributions are significantly different from a Maxwell-Boltzmann distribution corresponding to entirely thermal energy, and are moderately different from the energy distribution corresponding to the Siemens-Rasmussen approximation.