Hunting Antimatter Nuclei in Ultrarelativistic Heavy-Ion Collisions

Abstract

The transition from normal nuclear matter to the Quark-Gluon Plasma (QGP), a hot and dense partonic matter, has been predicted by the Lattice QCD. Relativistic heavy-ion collision creates suitable conditions for the formation of QGP, and indeed, mounting evidences suggest that the QGP matter has been produced in central Au + Au collisions at RHIC's top energies [1–4]. If compared to elementary particle collisions, nuclear collisions deposit large amount of energy into a more extended volume, allowing for the creation of a plasma containing roughly equal numbers of quarks and antiquarks. On the other hand, in contrast to the other extreme—the Big Bang, nuclear collisions produce negligible gravitational attraction and allow the QGP to expand rapidly. As the expansion slows down the plasma undergoes a transition into hadron gas, producing nucleons and their antiparticles. During the process, light antimatter nuclei can be formed by thermal production [5] or by coalescence [6]. The high temperature and high antibaryon density of relativistic heavy-ion collisions provide a favorable environment for both production mechanisms. Once light antimatter nuclei are formed, the relatively short-lived expansion in nuclear collisions allows antimatter to decouple quickly from matter, and avoid annihilation. Thus relativistic heavy-ion collision is an ideal venue to produce rare antimatter nuclei.