Speaker
Description
Hypernuclei are bound states of nucleons and hyperons, and thus naturally correlated hyperon-baryon systems. Hypernuclei are regarded a unique laboratory to study the hyperon-nucleon ($Y$-$N$) interaction. The $Y$-$N$ interaction is an important ingredient, not only in the equation-of-state (EoS) of astrophysical objects such as neutron stars, but also in the description of the hadronic phase of a heavy-ion collision. The strength of the $Y$-$N$ interaction can be investigated by measuring the properties of hypernuclei. Precise determination of hypernucei structure parameters, such as $\Lambda$ separation energy $B_{\Lambda}$, lifetime, and branching ratios, may also shed light on the role that two-body $Y$-$N$ and three-body $Y$-$N$-$N$ interactions play in the density regime of neutron stars.
In this talk, we report precision measurements of the lifetime of $^{3}_{\Lambda}\mathrm{H}$, $^{4}_{\Lambda}\mathrm{H}$ and $^{4}_{\Lambda}\mathrm{He}$ obtained from Au+Au collisions collected by STAR during the Beam Energy Scan Phase-II program. Hypernuclei are reconstructed via charged pion decay channels including both two-body and three-body decay modes. We also present the relative branching ratio $R_3$ of $^{3}_{\Lambda}\mathrm{H}$ and $^{4}_{\Lambda}\mathrm{H}$, where $R_3$ is the fraction of the two-body decay rate out of the sum of two-body and three-body decay rates. The results will be compared with model calculations and physics implications will be discussed.
