Speaker
Description
Recent relativistic heavy ion (RHI) collision experiments have extracted conflicting values of the hypertriton (${}_\Lambda^3\mathrm{H}$) lifetime ($\tau({}_\Lambda^3\mathrm{H})$). While the ALICE Collaboration's reported $\tau({}_\Lambda^3\mathrm{H})$ is comparable to the free $\Lambda$ lifetime, the STAR Collaboration's reported value is considerably shorter. A similarly large spread of values has been obtained also in earlier measurements.
Recently, we revisited theoretically this ${}_\Lambda^3\mathrm{H}$ lifetime puzzle [1], 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 $\Gamma({}_\Lambda^3\mathrm{H}\to{}^3\mathrm{He}+\pi^-)$. We found significant but opposing contributions arising from $\Sigma NN$ admixtures in ${}_\Lambda^3\mathrm{H}$ and from $\pi^- -{}^3\mathrm{He}$ final-state interaction, as well as substantial theoretical uncertainties attributed to (hyper)nuclear structure uncertainties. 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. The resulting $\tau({}_\Lambda^3\mathrm{H})$ varies strongly with the rather poorly known $\Lambda$ separation energy $E_{\mathrm{sep}}({}_\Lambda^3\mathrm{H})$ and it is possible to associate each one of the distinct RHI $\tau({}_\Lambda^3\mathrm{H})$ measurements with its own underlying value of $E_{\mathrm{sep}}({}_\Lambda^3\mathrm{H})$.
[1] A. Pérez-Obiol, D. Gazda, E. Friedman, A. Gal, Revisiting the hypertriton lifetime puzzle, Phys. Lett. B 811, 135916 (2020).
