Light nuclei production in pp and pA collisions in the Baryon Canonical Ensemble

TL;DR

This paper investigates light nuclei production in proton-proton and proton-lead collisions at the LHC using a thermal model with exact baryon number conservation, successfully describing some yields but highlighting potential non-equilibrium effects for certain nuclei.

Contribution

It extends the thermal hadron resonance gas model to include exact baryon number conservation and applies it to light nuclei production in small collision systems.

Findings

Good description of proton and deuteron yields as a function of multiplicity.

Yields of $^3$He and $^3_\Lambda$H are lower than model predictions at small multiplicities.

Possible non-equilibrium effects for $^3$He and $^3_\Lambda$H at low multiplicities.

Abstract

The increase in yields of light nuclei with charged particle multiplicity, as reported by the ALICE collaboration at CERN in p-p and p-Pb collisions at the LHC energy is investigated in the thermal hadron resonance gas model. The model is extended to account for exact baryon number conservation. The focus is on the production of protons, deuterons, $^3$He, and $^3_\Lambda$H. A very good description of proton and deuteron yields is obtained as a function of charged particle multiplicity in the mid-rapidity region using the same fixed temperature as in central Pb-Pb collisions. The yields of light nuclei $^3$He and $^3_\Lambda$H though qualitatively explained as a function of multiplicity, are lower than the model expectation. One of the possible reasons could be that for $^{3}$He and $^{3}_{\Lambda}$H, the chemical equilibrium is not yet reached at small multiplicities.