Conflicting values of the hypertriton lifetime $\tau({ }_\Lambda^3\mathrm{ H})$ 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 $\tau({ }_\Lambda^3\mathrm{ H})$ comes sufficiently close to the free-$\Lambda$ lifetime $\tau_\Lambda$,as expected naively for a very weakly bound $\Lambda$ in ${ }_\Lambda^3\mathrm{ H}$. We revisited theoretically this ${ }_\Lambda^3\mathrm{ H}$ lifetime puzzle, using ${ }_\Lambda^3\mathrm{ H}$ and ${ }^3\mathrm{ He}$ 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 $\Gamma({ }_\Lambda^3\mathrm{ H}\to{ }^3\mathrm{ He}+\pi^-)$. 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. 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 thus possible to associate each one of the distinct RHI $\tau({ }_\Lambda^3\mathrm{ H})$ measurements with its own underlying value of $E_{ \mathrm{ sep}}({ }_\Lambda^3\mathrm{ H})$.
Categories: nucl-th hep-ph nucl-ex