Lifetime of the hypertriton

Abstract

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 $E_{\mathrm{sep}}({}_{\Lambda }^3\mathrm{H})$.

arXiv commentInvited talk given at the 14th International Conference on Hypernuclear and Strange Particle Physics (HYP2022), Prague, Czech Republic, June 27 - July 1, 2022. A slightly updated version of the published proceedings contribution

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• Letter of Intent: the NA60+ experiment