Effects of in-medium cross sections and optical potential on thermal-source formation in p+{sup 197}Au reactions at 6.2-14.6 GeV/c

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 $p+^{197}\mathrm{Au}$ reaction at $6.2\char21{}14.6\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}∕c$. 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 $25\phantom{\rule{0.3em}{0ex}}\mathrm{fm}∕c$ 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 $65\phantom{\rule{0.3em}{0ex}}\mathrm{fm}∕c$ 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, $\ensuremath{\rho}∕{\ensuremath{\rho}}_{0}\ensuremath{\sim}1∕4\char21{}1∕3$ for central collisions, and low-to-moderate excitation, i.e., the region of nuclear liquid-gas phase transition.