Why Do Light Nuclei Survive at the Large Hadron Collider?

Abstract

Light nuclei and antinuclei, such as deuterons, are produced abundantly at the Large Hadron Collider (LHC) in hadronic and nuclear collisions. Even though their binding energies are only a few MeV, they survive in the extremely high temperatures of the order of a few hundred MeV. This contradiction, often referred to as ``Snowballs in Hell'', has become a sharp test of how quantum chromodynamics (QCD) turns quarks and gluons into composite matter. Strikingly, two very different frameworks can reproduce the same inclusive yields, i.e., late-stage nucleon coalescence, where nuclei form from nearby nucleons as the system dilutes, and statistical thermal models, where nuclei emerge as part of an equilibrated hadronization chemistry at a temperature close to 155 MeV. Here, we review how recent LHC measurements and model developments are shifting the question--from whether light nuclei are produced, to when and how they form, with broader implications for QCD matter and cosmic-ray antinuclei searches.