On the origin of nuclei in hadronic collisions: nuclear coalescence from correlation functions

The production of nuclei (deuterons, He3, He4, …) at the LHC has a puzzling feature. Nuclei yields are consistent with a simple thermal Boltzman factor, with the same temperature that describes mesons and nucleons. This thermal fit spans 9 orders of magnitude in yield. But how can a deuteron with a binding energy of 2.2 MeV, participate in a thermal distribution with characteristic particle energies of 100 MeV? Even more confusing, given the deuteron charge radius of 2.1 fm, how can it participate in a thermal state in proton-proton collisions with coherence length of just 1-2 fm? I will explain how quantum mechanics offers an elegant solution of this puzzle, via nuclear coalescence. A key prediction of this idea is a model-independent relation between nuclear yields and momentum correlations of nucleon pairs. A second prediction concerns hyper-tritons, for which new experimental data from proton-proton collisions has recently finally become available.