Lifetime of the hypertriton

Conflicting values of the hypertriton lifetime $\tau ({}_{\mathrm{\Lambda }}^3\mathrm{H})$ were derived in relativistic heavy ion (RHI) collision experiments over the last decade. A very recent ALICE Collaboration measurement is the only experiment where the reported $\tau ({}_{\mathrm{\Lambda }}^3\mathrm{H})$ comes sufficiently close to the free-$\mathrm{\Lambda }$ lifetime ${\tau }_{\mathrm{\Lambda }}$,as expected naively for a very weakly bound $\mathrm{\Lambda }$ in ${}_{\mathrm{\Lambda }}^3\mathrm{H}$. We revisited theoretically this ${}_{\mathrm{\Lambda }}^3\mathrm{H}$ lifetime puzzle, using ${}_{\mathrm{\Lambda }}^3\mathrm{H}$ and ${}^3\mathrm{H}\mathrm{e}$ wave functions computed within the abinitio no-core shell model employing interactions derived from chiral effective field theory to calculate the two-body decay rate $\mathrm{\Gamma }({}_{\mathrm{\Lambda }}^3\mathrm{H}\to {}^3\mathrm{H}\mathrm{e}+{\pi }^{-})$. We found significant but opposing contributions arising from $\mathrm{\Sigma }NN$ admixtures in ${}_{\mathrm{\Lambda }}^3\mathrm{H}$ and from ${\pi }^{-}-{}^3\mathrm{H}\mathrm{e}$ final-state interaction. To derive $\tau ({}_{\mathrm{\Lambda }}^3\mathrm{H})$, we evaluated the inclusive ${\pi }^{-}$ decay rate ${\mathrm{\Gamma }}_{{\pi }^{-}}({}_{\mathrm{\Lambda }}^3\mathrm{H})$ by using the measured branching ratio $\mathrm{\Gamma }({}_{\mathrm{\Lambda }}^3\mathrm{H}\to {}^3\mathrm{H}\mathrm{e}+{\pi }^{-})\mathrm{/}{\mathrm{\Gamma }}_{{\pi }^{-}}({}_{\mathrm{\Lambda }}^3\mathrm{H})$ and added the ${\pi }^0$ contributions through the $\mathrm{\Delta }I=\frac{1}{2}$ rule. The resulting $\tau ({}_{\mathrm{\Lambda }}^3\mathrm{H})$ varies strongly with the rather poorly known $\mathrm{\Lambda }$ separation energy $E_{\mathrm{s}\mathrm{e}\mathrm{p}}({}_{\mathrm{\Lambda }}^3\mathrm{H})$ and it is thus possible to associate each one of the distinct RHI $\tau ({}_{\mathrm{\Lambda }}^3\mathrm{H})$ measurements with its own underlying value of $E_{\mathrm{s}\mathrm{e}\mathrm{p}}({}_{\mathrm{\Lambda }}^3\mathrm{H})$.