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 $\mathrm{\Delta }{Y}_{\pi }$. In contrast, in a thermal model, cluster production is independent on $\mathrm{\Delta }{Y}_{\pi }$. The observation of a maximum deuteron (cluster) yield as function of $\mathrm{\Delta }{Y}_{\pi }$ provides confirmation of the coalescence mechanism.