Production of antimatter $^{5,6}$Li nuclei in central Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV

Combining the covariant coalescence model and a blast-wave-like analytical parametrization for (anti-)nucleon phase-space freezeout configuration, we explore light (anti-)nucleus production in central Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV. Using the nucleon freezeout configuration (denoted by FO1) determined from the measured spectra of protons (p), deutrons (d) and $^{3}$He, we find the predicted yield of $^{4}$He is significantly smaller than the experimental data. We show this disagreement can be removed by using a nucleon freezeout configuration (denoted by FO2) in which the nucleons are assumed to freeze out earlier than those in FO1 to effectively consider the effect of large binding energy value of $^{4}$He. Assuming the binding energy effect also exists for the production of $^5\text{Li}$, $^5\overline{\text{Li}}$, $^6\text{Li}$ and $^6\overline{\text{Li}}$ due to their similar binding energy values as $^{4}$He, we find the yields of these heavier (anti-)nuclei can be enhanced by a factor of about one order, implying that although the stable (anti-)$^6$Li nucleus is unlikely to be observed, the unstable (anti-)$^5$Li nucleus could be produced in observable abundance in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV where it may be identified through the p-$^4\text{He}$ ($\overline{\text{p}}$-$^4\overline{\text{He}}$) invariant mass spectrum. The future experimental measurement on (anti-)$^5\text{Li}$ would be very useful to understand the production mechanism of heavier antimatter.

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