Collective motion in selected central collisions of Au on Au at 150AMeV

Generalized isoscaling of isotopic distributions

“…) is fragment yield ratio of the ground states for isotope pairs (3,4) and (1,2), a is a ground state spin factor. Information on the four thermometers studied in the present work is listed in …”

“…At incident energies in excess of about E/A=30 MeV, a rapid collective expansion of the combined system may occur during the later stages of a central collision between heavy nuclei [1,2]. At densities less than about 1/3 saturation density such systems disassemble into a mixture of fragments and light particles; the duration of fragment emission is of the order of 100 fm/c [3,4].…”

“…After correction for collective expansion, for example, calculated excitation energies for peripheral collisions at high energies must be further reduced by roughly 30% to reproduce experimental data and larger corrections are estimated for energetic central collisions [2,7,19,27]. Collective motion, pre-equilibrium emission and Coulomb barrier fluctuations increase significantly the temperatures deduced from kinetic energy spectra [1][2][3]12,19] while secondary decay modifies the temperatures deduced from excited state populations and isotope ratios [21,22]. Resolving these problems is an important priority.…”

Isospin Tracing: A Probe of Nonequilibrium in Central Heavy-Ion Collisions

“…An understanding of all these effects is a prerequisite for a quantitative extraction of the EOS from nucleus-nucleus collisions.Experimental observations of non-equilibrium in relativistic heavy-ion collisions were concentrated, up to now, on the measurement of the momentum distribution of the products emerging from a mid-rapidity "source" of symmetric colliding systems. Observables of interest were the width of rapidity distributions [3,5] or the overall shape of the source [6,7]. The sensitivity of such observables is however reduced by effects like rescattering during the late phase of expansion.In order to extract, in a model independent approach, direct experimental information on non-equilibrium we have designed a new type of high precision measurement which makes use of the isospin (N/Z) degree of freedom.…”

“…Experimental observations of non-equilibrium in relativistic heavy-ion collisions were concentrated, up to now, on the measurement of the momentum distribution of the products emerging from a mid-rapidity "source" of symmetric colliding systems. Observables of interest were the width of rapidity distributions [3,5] or the overall shape of the source [6,7]. The sensitivity of such observables is however reduced by effects like rescattering during the late phase of expansion.…”