Speaker
Description
Hypernuclei, which are special nuclei formed by nucleon cores and hyperons, are ideal platforms to study the hyperon-nucleon interactions. The $\Lambda$-binding energies ($B_{\Lambda}$) of hypernuclei are direct observables encoding the ΛN and ΛNN interactions, which are relevant to understanding the ``hyperon puzzle'' in neutron stars. However, the measurements on the $B_{\Lambda}$ of light hypernuclei are still controversial. A recent measurement by the A1 Collaboration reported $B_{\Lambda}$($^{3}_{\Lambda}{\rm H}$) = 523 $\pm$ 13 (stat.) $\pm$ 75 (syst.) keV, substantially larger than the historical world-average value of approximately 120 keV. For the mirror hypernuclei pair $^{4}_{\Lambda}{\rm H}$ and $^{4}_{\Lambda}{\rm He}$, the charge-symmetry breaking (CSB) manifests itself as a difference in their $B_{\Lambda}$. The CSB in the ground state and the excited state reveal the difference between the $\Lambda$-p and $\Lambda$-n interactions. Together, these considerations motivate independent high-precision measurements.
As part of the STAR fixed target program, the STAR detector collected data in Au+Au collisions at $\sqrt{s_{NN}}=3~$GeV. The high production yield of light hypernuclei provides an opportunity to measure their $B_{\Lambda}$ precisely. In this talk, we will present the measurement of the $B_{\Lambda}$ of $^{3}_{\Lambda}{\rm H}$, $^{4}_{\Lambda}{\rm H}$, and $^{4}_{\Lambda}{\rm He}$ with about 2 billion Au+Au collision events at $\sqrt{s_{NN}}=3~$GeV collected in 2021. The results will be presented together with the methods, calibrations, and systematic uncertainties of the measurements.
