Probing configuration of $α$ clusters with spectator particles in relativistic heavy-ion collisions

Abstract

We propose to use spectator particle yield ratios to probe the configuration of $α$ clusters in $^{12}$C and $^{16}$O by their collisions at RHIC and LHC energies. The idea is illustrated based on initial density distributions with various $α$-cluster configurations generated by a microscopic cluster model, and without $α$ clusters from mean-field calculations. The multifragmentation of the spectator matter produces more spectator light nuclei including $α$ clusters in collisions of nuclei with chain structure of $α$ clusters, compared to those of nuclei with a more compact structure. The yield ratio of free spectator neutrons to spectator particles with mass-to-charge ratio $A/Z=2$ scaled by their masses can be practically measured by the zero-degree calorimeter (ZDC) at RHIC and LHC, serving as a clean probe free from modeling the complicated dynamics at midrapidities.