Speaker
Description
Studies of light nucleus production, including deuterons, and helium nuclei, in heavy-ion collisions are essential for understanding the dynamics of nuclear matter under extreme conditions and provide valuable insights into the underlying equation of state. Compound yield ratios, such as $\rm N_t \times N_p/N_d^2$ and $\rm N_{^4He} \times N_p / (N_{^3He} \times N_d)$, have been proposed as probes of local baryon-density fluctuations and possible critical behavior in quantum chromodynamics (QCD). In addition, the yields and ratios of light nuclei can help constrain thermal-statistical and coalescence descriptions. The larger STAR BES-II datasets extended energy coverage toward higher net-baryon density, and improved detector capabilities enable more precise and comprehensive measurements than BES-I.
In this talk, we will present the energy dependence of the coalescence parameters $(B_\mathrm{A})$ and particle yield ratios involving p, d, $\rm ^3He$, and $\rm ^4He$ in Au+Au collisions at BES-II energies of $\sqrt{s_{\rm NN}}$ = $3-27$ GeV. The uncertainties on yields and ratios in BES-II are reduced by a factor of approximately 3-5 compared to BES-I. The thermal model overestimates the $N_{^3\mathrm{He}}/N_p$ and $N_{^4\mathrm{He}}/N_p$ ratios, with discrepancies increasing toward lower collision energies and reaching up to 50%. In contrast, the coalescence calculation provides a better description for nuclei with $A \leq 3$, while underpredicting $^4\mathrm{He}$.
