${}_{\mathrm{\Lambda }}^3\mathrm{H}$ and ${}_{\bar{\mathrm{\Lambda }}}^3\bar{\mathrm{H}}$ production in Pb-Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}$ = 2.76 TeV

The production of the hypertriton nuclei ${}_{\mathrm{\Lambda }}^3\mathrm{H}$ and ${}_{\bar{\mathrm{\Lambda }}}^3\bar{\mathrm{H}}$ has been measured for the first time in Pb-Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}$ = 2.76 TeV with the ALICE experiment at LHC energies. The total yield, d$N$/d$y$ $\times $\mathrm{B}\mathrm{.}\mathrm{R}\mathrm{.}${\left( ^{3}{\Lambda}\mathrm H \rightarrow ^{3}$\mathrm{H}\mathrm{e}$,\pi^{-} \right)} = \left( 3.86 \pm 0.77 ($\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.}$) \pm 0.68 ($\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}$)\right) \times 10^{-5}$ in the 0-10% most central collisions, is consistent with the predictions from a statistical thermal model using the same temperature as for the light hadrons. The coalescence parameter $B_3$ shows a dependence on the transverse momentum, similar to the $B_2$ of deuterons and the $B_3$ of ${}^3\mathrm{H}\mathrm{e}$ nuclei. The ratio of yields $S_3$ = ${}_{\mathrm{\Lambda }}^3\mathrm{H}$/(${}^3\mathrm{H}\mathrm{e}$ $\times \mathrm{\Lambda }\mathrm{/}\mathrm{p}$) was measured to be $S_3$ = 0.60 $\pm$ 0.13 (stat.) $\pm$ 0.21 (syst.) in 0-10% centrality events; this value is compared to different theoretical models. The measured $S_3$ is fully compatible with thermal model predictions. The measured ${}_{\mathrm{\Lambda }}^3\mathrm{H}$ lifetime, $ \tau = 181^{+54}_{-39} ($\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.}$) \pm 33 ($\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}$)\ $\mathrm{p}\mathrm{s}$$iscompatiblewithin1$\sigma$ with the world average value.