Abstract
The production of light nuclei in relativistic heavy-ion collisions is well described by both the thermal model, where light nuclei are in equilibrium with hadrons of all species present in a fireball, and by the coalescence model, where light nuclei are formed due to final-state interactions after the fireball decays. We present and critically discuss the two models and further on we consider two proposals to falsify one of the models. The first proposal is to measure a yield of exotic nuclide 4Li and compare it to that of 4He. The ratio of yields of the nuclides is quite different in the thermal and coalescence models. The second proposal is to measure a hadron-deuteron correlation function which carries information whether a deuteron is emitted from a fireball together with all other hadrons, as assumed in the thermal model, or a deuteron is formed only after nucleons are emitted, as in the coalescence model. The p − 3He correlation function is of interest in context of both proposals: it is needed to obtain the yield of 4Li which decays into p and 3He, but the correlation function can also tell us about an origin of 3He.
Highlights
Production of light nuclei in nucleus-nucleus collisions has been studied for decades but plethora of experimental results from Relativistic Heavy Ion Collider (RHIC) [1,2] and Large Hadron Collider (LHC) [3,4,5] have revived an interest in the problem and attracted a lot of attention
At high-energy collisions light nuclei occur as fragments of incoming nuclei, as at low-energy collisions, but we deal with a genuine production process – the energy released in a collision is converted into masses of baryons and antibaryons which form nuclei and antinuclei
We close the presentation of the coalescence model by saying that whenever we refer to the model we keep in mind the expression (1) with the formation rate given by equation (5)
Summary
Production of light nuclei in nucleus-nucleus collisions has been studied for decades but plethora of experimental results from Relativistic Heavy Ion Collider (RHIC) [1,2] and Large Hadron Collider (LHC) [3,4,5] have revived an interest in the problem and attracted a lot of attention. The observation has been recently confirmed [12,19], using a more refined version of the coalescence model [34,35,36,37,38], which properly treats a quantum-mechanical character of the formation process of light nuclei The aim of this short but rather pedagogical review is to critically discuss the thermal and coalescence models of production of light nuclei in relativistic heavyion collisions. The second proposal to falsify one of the models relies on the observation [21] that a hadron-deuteron correlation function can tell us whether deuterons are directly emitted from a fireball or they are formed later on due to final-state interactions. If one assumes that 3He is emitted directly from the fireball the source radius inferred from the p−3He correlation function is smaller by the factor 3/2 than that corresponding to the scenario where nucleons emitted from the fireball form the nuclide 3He due to final-state interactions.
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