Investigating the cluster production mechanism with isospin triggering: Thermal models versus coalescence models

Isospin triggering allows to distinguish coalescence from thermal production of light clusters in heavy ion collisions. Triggering on $Y(\pi^-) - Y(\pi^+)$ allows to select very neutron or proton rich final states. The deuteron (cluster) production with coalescence ($d \propto n \cdot p$) leads then to an inverse parabolic dependence of the deuteron yield on $\Delta Y_{\pi}$. In contrast, in a thermal model, cluster production is independent on $\Delta Y_{\pi}$. The observation of a maximum deuteron (cluster) yield as function of $\Delta Y_{\pi}$ provides confirmation of the coalescence mechanism.