Nucleosynthesis in heavy-ion collisions at the LHC via the Saha equation

Kai Gallmeister,Carsten Greiner,Volodymyr Vovchenko,Jürgen Schaffner-Bielich

doi:10.1016/j.physletb.2019.135131

Kai Gallmeister, Carsten Greiner + Show 2 more

Open Access

https://doi.org/10.1016/j.physletb.2019.135131

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Abstract

The production of light (anti-)(hyper-)nuclei in heavy-ion collisions at the LHC is considered in the framework of the Saha equation, making use of the analogy between the evolution of the early universe after the Big Bang and that of “Little Bangs” created in the lab. Assuming that disintegration and regeneration reactions involving light nuclei proceed in relative chemical equilibrium after the chemical freeze-out of hadrons, their abundances are determined through the famous cosmological Saha equation of primordial nucleosynthesis and show no exponential dependence on the temperature typical for the thermal model. A quantitative analysis, performed using the hadron resonance gas model in partial chemical equilibrium, shows agreement with experimental data of the ALICE collaboration on d, 3He, HΛ3, and 4He yields for a very broad range of temperatures at T≲155 MeV. The presented picture is supported by the observed suppression of resonance yields in central Pb–Pb collisions at the LHC.

Highlights

The yields of light(hyper-)nuclei such as deuteron (d), helium-3 (3He), hypertriton (3 H), and helium-4 (4He) have recently been measured in Pb-Pb collisions at the LHC by the ALICE collaboration [1,2,3]
Our results provide a natural explanation for this phenomenon in terms of the Saha equation treatment of the break-up and regeneration reactions X + A ↔ X + i Ai involving light nuclei
We analyzed the production of light(hyper-)nuclei in heavy-ion collisions at the LHC in the framework of the Saha equation, making use of the intimate and illustrative analogy between the evolution of the early universe after the Big Bang and that of “Little Bangs” created in the lab

Summary

Introduction

The yields of light (anti-)(hyper-)nuclei such as deuteron (d), helium-3 (3He), hypertriton (3 H), and helium-4 (4He) have recently been measured in Pb-Pb collisions at the LHC by the ALICE collaboration [1,2,3]. The measured yields have been observed to agree remarkably well with a thermal model calculation at a temperature Tch 155 MeV of the conventional chemical freeze-out of hadrons [21,22,23], while the available transverse momentum spectra of both nuclei and stable hadrons are characterized by a lower kinetic freeze-out temperature Tkin 100 − 115 MeV [1]. These observations suggest that certain thermal aspects are present in the production mechanism of loosely-bound objects. A crucial new point here is the role of the mesonic component, which dominates at the LHC conditions and resembles photons in the early universe

Saha equation

Full numerical calculation

Findings

Summary and conclusions