Noncentral heavy-ion collisions produce hot and dense nuclear matter with significant fluid vorticity, which can induce global polarizations or alignments of particles with nonzero spins along the direction of the total orbital angular momentum. This phenomenon has been observed for hyperons and vector mesons in experiments. In the present study, we demonstrate that polarized nucleons lead to global spin alignment of the unstable nucleus ${}^4\mathrm{Li}$, which can be measured through its strong decays via ${}^4\mathrm{Li}\to {}^3\mathrm{He}+p$. Assuming that ${}^4\mathrm{Li}$ is formed through the coalescence of polarized nucleons at kinetic freeze out, we obtain the angular distribution of the daughter particle ${}^3\mathrm{He}$ in the rest frame of the polarized ${}^4\mathrm{Li}$. Taking kinetic freeze-out nucleons from an isotropic and thermalized fireball of constant vorticity and including quantum corrections up to ${\hslash }^2$ in the coalescence calculation through the Moyal star product, we find that the angular distribution of ${}^3\mathrm{He}$ has a $cos\left(2{\theta }^{*}\right)$ dependence with ${\theta }^{*}$ being its angle with respect to the polarization direction of ${}^4\mathrm{Li}$. We also find that the ${}^3\mathrm{He}$ angular distribution depends on both the vorticity and the polarization of kinetic freeze-out nucleons. Future measurements on the spin alignment of ${}^4\mathrm{Li}$ in heavy-ion collisions thus offer a promising method to probe the spin dynamics, vortical structure, and spin-dependent equation-of-state of the nuclear matter produced in these collisions.

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• Particle & resonance production
• Polarization phenomena
• Quark-gluon plasma
• Transport in heavy-ion collisions