Effects of in-medium cross sections and optical potential on thermal-source formation in p+Au-197 reactions at 6.2-14.6 GeV/c
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Effects of in-medium cross sections and of optical potential on preequilibrium emission and on formation of a thermal source are investigated by comparing the results of transport simulations with experimental results from the p +197Au reaction at 6.2-14.6 GeV/c. The employed transport model includes light-composite-particle production and allows for inclusion of in-medium particle-particle cross-section reduction and of momentum dependence in the particle optical potentials. Compared to the past, the model incorporates improved parametrizations of elementary high-energy processes. The simulations indicate that the majority of energy deposition occurs during the first 25 fm/c of a reaction. This is followed by a preequilibrium emission and readjustment of system density and momentum distribution toward an equilibrated system. Within different variants of calculations, the best agreement with data, on the d/p and t/p yield ratios and on the residue mass and charge numbers, is obtained at the time of about 65 fm/c from the start of a reaction, for simulations employing reduced in-medium cross sections and momentum-dependent optical potentials. By that time, the preequilibrium nucleon and cluster emission, as well as mean field readjustments, drive the system to a state of depleted average density, /01/4-1/3 for central collisions, and low-to-moderate excitation, i.e., the region of nuclear liquid-gas phase transition.
