Antimatter $^4_{\Lambda}$H Hypernucleus Production and the $^3_{\Lambda}$H/$^3$He Puzzle in Relativistic Heavy-Ion Collisions

TL;DR

This paper explains the production ratios of hypernuclei and their antimatter counterparts in heavy-ion collisions using a covariant coalescence model, highlighting the importance of earlier (anti-)$\Lambda$ freezeout and its impact on hypernucleus yields.

Contribution

It introduces a covariant coalescence model that accounts for different freezeout times of (anti-)$\Lambda$ particles, explaining hypernucleus production ratios and predicting measurable antimatter hypernuclei.

Findings

The yield ratio $^3_{\Lambda}$H/$^3$He can be explained by earlier (anti-)$\Lambda$ freezeout.

Earlier (anti-)$\Lambda$ freezeout enhances $^4_{\Lambda}$H production.

Antimatter hypernucleus $^4_{\overline{\Lambda}}$H could be as abundant as $^4 ext{ extoverline{He}}$, serving as a new antimatter candidate.

Abstract

We show that the measured yield ratio $^3_{\Lambda}$H/$^3$He ($^3_{\overline{\Lambda}}\overline{\text{H}}$/$^3\overline{\text{He}}$) in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV and in Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV can be understood within a covariant coalescence model if (anti-)$\Lambda$ particles freeze out earlier than (anti-)nucleons but their relative freezeout time is closer at $\sqrt{s_{NN}}=2.76$ TeV than at $\sqrt{s_{NN}}=200$ GeV. The earlier (anti-)$\Lambda$ freezeout can significantly enhance the yield of (anti)hypernucleus $^4_{\Lambda}$H ($^4_{\overline{\Lambda}}\overline{\text{H}}$), leading to that $^4_{\overline{\Lambda}}\overline{\text{H}}$ has a comparable abundance with $^4\overline{\text{He}}$ and thus provides an easily measured antimatter candidate heavier than $^4\overline{\text{He}}$. The future measurement on $^4_{\Lambda}$H ($^4_{\overline{\Lambda}}\overline{\text{H}}$) would be very useful to understand the (anti-)$\Lambda$ freezeout dynamics and the production mechanism of (anti)hypernuclei in relativistic heavy-ion collisions.