Speaker
Description
Over the last decade, conflicting values of the hypertriton (${}_\Lambda^3\mathrm{H}$) lifetime ($\tau({}_\Lambda^3\mathrm{H})$) were extracted from relativistic heavy-ion (RHI) collision experiments, ranging from values compatible with the free-$\Lambda$ lifetime ($\tau_\Lambda$)-as expected naively for a very weakly bound $\Lambda$ in ${}_\Lambda^3\mathrm{H}$-to lifetimes as short as $\tau({}_\Lambda^3\mathrm{H})\approx (0.4–0.7)\tau_\Lambda$. A similarly large spread of values has been obtained also in earlier measurements.
Recently, we revisited theoretically this ${}_\Lambda^3\mathrm{H}$ lifetime puzzle, using ${}_\Lambda^3\mathrm{H}$ and ${}^3\mathrm{He}$ wave functions computed within the ab initio no-core shell model employing interactions derived from chiral effective field theory to calculate the two-body decay rate $\Gamma({}_\Lambda^3\mathrm{H}\to{}^3\mathrm{He}+\pi^-)$. To derive $\tau({}_\Lambda^3\mathrm{H})$, we evaluated the inclusive $\pi^-$ decay rate $\Gamma_{\pi^-}({}_\Lambda^3\mathrm{H})$ by using the measured branching ratio $\Gamma({}_\Lambda^3\mathrm{H}\to{}^3\mathrm{He}+\pi^-)/\Gamma_{\pi^-}({}_\Lambda^3\mathrm{H})$ and added the $\pi^0$ contributions through the $\Delta I = \frac{1}{2}$ rule. We found significant but opposing contributions to $\tau({}_\Lambda^3\mathrm{H})$ arising from $\Sigma NN$ admixtures in ${}_\Lambda^3\mathrm{H}$ and from $\pi^- -{}^3\mathrm{He}$ final-state interaction [1], as well as substantial theoretical uncertainties inherent in the employed nuclear and hypernuclear interaction models [2]. Since $\tau({}_\Lambda^3\mathrm{H})$ was found to be strongly correlated with the $\Lambda$ separation energy in ${}_\Lambda^3\mathrm{H}$ ($B_\Lambda$), the value of which suffers from large experimental as well as theoretical uncertainties, we conclude that none of the conflicting RHI measured lifetime values can be excluded, but rather implies its own constraint on $B_\Lambda$.
[1] A. Pérez-Obiol, D. Gazda, E. Friedman, A. Gal, Revisiting the hypertriton lifetime puzzle, Phys. Lett. B 811, 135916 (2020)
[2] D. Gazda, A. Pérez-Obiol, E. Friedman, A. Gal, Hypertriton lifetime, Phys. Rev. C 109, 024001 (2024)
