Confronting the production mechanisms of nuclei with deuteron and proton-triggered balance functions

TL;DR

Addressing how light nuclei form in ultra-high-energy pp collisions, the paper tests whether proton- and deuteron-triggered balance functions can distinguish coalescence from thermal production mechanisms. It compares a coalescence implementation in PYTHIA with a thermal hadronization description in Thermal FIST, using proton- and deuteron-triggered balance functions in rapidity. A key finding is that, while the two models yield the same simple relation between deuteron- and proton-triggered balance functions, they exhibit a strikingly different dependence on the trigger transverse momentum $p_{T}^{\mathrm{trig}}$, providing a discriminating observable beyond yields. Additional results show deuteron–pion balances vanish due to baryon-number conservation and isospin symmetry, and that correlation volume and temperature modulations shape the balance functions in Thermal FIST. The study proposes exploiting Run 3 ALICE data to test hadronization mechanisms and to probe the microscopic origins of light nuclei formation.

Abstract

In ultra high-energy collisions, nuclei with very low binding energies are not expected to survive the dense and hot final state environment. The traditional view has therefore been that nuclei form via coalescence after the hot environment has dissipated. However, statistical thermal models, where hadrons are produced from a fireball at thermal equilibrium, can describe the relative abundances of light nuclei in pp and heavy-ion collisions at the LHC equally well. In this paper we investigate if balance functions triggered by protons and deuterons can be used to distinguish between the two production mechanisms. The coalescence model is investigated using PYTHIA, while the statistical thermal model is examined using the Thermal FIST package. We find that for both models the same simple relation between proton and deuteron triggered balance functions is applicable. However, there is a striking difference between the two models when the transverse momentum of trigger particles is varied. This dependence offers a promising observable to discriminate between the two production scenarios that goes beyond nuclei production. Furthermore, we find that deuteron-meson balance functions vanish identically for both models due to baryon number conservation and isospin symmetry.

Figures (9)

• Figure 1: A representative plot of the associated yield of antiprotons per triggered protons in pp collisions at $\sqrt{s}$ = 13 TeV.
• Figure 2: Depiction of analysis methodology to estimate the proton and deuteron-triggered balance functions
• Figure 3: Comparison of the balance function of triggered protons (left) and triggered deuterons (right) obtained from PYTHIA and Thermal FIST models.
• Figure 4: Comparison of the balance function of triggered protons and triggered deuterons divided by two obtained from PYTHIA (left) and Thermal FIST (right) models.
• Figure 5: Transverse momentum dependence of the balance function of triggered protons and triggered deuterons from PYTHIA (left) and Thermal FIST (right) models.