Effects of a first-order QCD phase transition on light nucleus production

Using an extended Polyakov-looped Nambu--Jona-Lasinio (PNJL) model to describe the baryon density fluctuations of quark matter along the isentropic trajectories corresponding to different $s/\rho_B$ values extracted from Au+Au collisions at energies $\sqrt{s_{NN}} = 7.7-200$ GeV, we investigate the effects of the first-order phase transition on the light nucleus yield ratio $N_t \times N_p/N_d^2$. The results indicate that the second-order scaled density moment $y_2$, used to quantify density fluctuations, rapidly increases to form a peak when the isentropic trajectories pass through the phase coexistence region. We extract the yield ratios $N_t\times N_p/N_d^2$ at chemical freeze-out from the isentropic trajectories at different collision energies and found significant enhancements at 19.6 GeV and 27 GeV. This is similar to the trends observed by the STAR experiment, suggesting that the enhancements in the yield ratios $N_t\times N_p/N_d^2$ observed in the STAR experiment could be explained by the density fluctuations generated in the first-order phase transition region.