Influence of coalescence parameters on the production of protons and Helium-3 fragments

Abstract

The time evolution of protons and $^3$He fragments from Au+Au/Pb+Pb reactions at 0.25, 2, and 20 GeV$/$nucleon is investigated with the potential version of the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model combined with the traditional coalescence afterburner. In the coalescence process, the relative distance $R_0$ and relative momentum $P_0$ are surveyed in the range of 3-4 fm and 0.25-0.35 GeV$/$c, respectively. For both clusters, a strong reversed correlation between $R_0$ and $P_0$ is seen and it is time-dependent as well. For protons, the accepted ($R_0$, $P_0$) bands lie in the time interval 30-60 fm$/$c, while for $^3$He, a longer time evolution (at about 60-90 fm$/$c) is needed. Otherwise, much smaller $R_0$ and $P_0$ values should be chosen. If we further look at the rapidity distributions from both central and semi-central collisions, it is found that the accepted [$t_{\rm cut}, (R_0, P_0$)] assemble can provide consistent results for proton yield and collective flows especially at mid-rapdities, while for $^3$He, the consistency is destroyed at both middle and projectile-target rapidities.