Light-nuclei production in pp and pA collisions in the baryon canonical ensemble approach

The increase in yields of light nuclei with charged particle multiplicity, as reported by the ALICE Collaboration at CERN in $p\text{\ensuremath{-}}p$ and $p$-Pb collisions at the Large Hadron Collider 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, $^{3}\mathrm{He}$, and $_{\mathrm{\ensuremath{\Lambda}}}^{3}\mathrm{H}$. A very good description of proton and deuteron yields is obtained as a function of charged particle multiplicity in the midrapidity region using the same fixed temperature as in central Pb-Pb collisions. The yields of light nuclei $^{3}\mathrm{He}$ and $_{\mathrm{\ensuremath{\Lambda}}}^{3}\mathrm{H}$, though qualitatively explained as a function of multiplicity, are lower than the model expectation. One of the possible reasons could be that for $^{3}\mathrm{He}$ and $_{\mathrm{\ensuremath{\Lambda}}}^{3}\mathrm{H}$, the chemical equilibrium is not yet reached at small multiplicities.