Asymmetry of velocity distributions in peripheral collisions at Fermi energies

TL;DR

This paper investigates the asymmetry in velocity distributions of projectile fragments in heavy-ion collisions at Fermi energies, combining transport model calculations with experimental data to understand the contributions of direct and dissipative processes.

Contribution

It introduces a detailed analysis of velocity distribution asymmetry using transport models and empirical interpretation, linking the shape of deflection functions to yield ratios.

Findings

Velocity distributions consist of direct and dissipative components.

Transport calculations accurately describe dissipative contributions.

The ratio of contributions depends on the deflection function shape.

Abstract

Asymmetry of the velocity distributions of projectile like fragments produced in heavy-ion collisions is discussed. The calculations made in transport model approach (the solution of Vlasov kinetic equation with the collisions term) are compared with experimental data for the reactions $^{22}Ne$ ($40 A\cdot$MeV) + $^{9}$Be and $^{18}$O ($35 A\cdot$MeV) + $^9$Be ($^{181}$Ta) at forward angles. It is found that the velocity distributions appear to be composed of two contributions: a direct component centered at beam velocity and a dissipative component at lower energies, leading to an asymmetry of the velocity distributions. The direct component is interpreted empirically in the Goldhaber model, and the widths and centroids of the distributions are extracted. The remaining dissipative (also called deep-inelastic) contributions are then well described by the transport calculations. It is shown that the ratio of yields of direct and dissipative contributions, which determines the asymmetry of velocity distribution, depends on the shape of the deflection function.