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arXiv · 2006.16718

Revisiting the hypertriton lifetime puzzle

A. Pérez-Obiol·D. Gazda·E. Friedman·A. Gal
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Abstract

Conflicting values of the hypertriton ($_Λ^{3}$H) lifetime were extracted in recent relativistic heavy-ion collision experiments. The ALICE Collaboration's reported $_Λ^{3}$H lifetime $τ(_Λ^{3}$H) is compatible within measurement uncertainties with the free $Λ$ lifetime $τ_Λ$, as naively expected for a loosely bound $Λ$ hyperon in $_Λ^{3}$H, whereas STAR's reported range of $τ(_Λ^{3}$H) values is considerably shorter: $τ_{\rm STAR}(_Λ^{3}$H)$\sim$(0.4-0.7)$τ_Λ$. This $_Λ^{3}$H lifetime puzzle is revisited theoretically using $_Λ^{3}$H three-body wavefunctions generated in a chiral effective field theory approach to calculate the decay rate $Γ(_Λ^{3}$H$\,\to ^3$He$\,+π^-$). Significant but opposing contributions arise from $ΣNN$ admixtures in $_Λ^{3}$H and from $π^-$-$^3$He final-state interaction. Evaluating the inclusive $π^-$ decay rate $Γ_{π^-}(_Λ^{3}$H) via a branching ratio $Γ(_Λ^{3}$H$\,\to ^{3}$He+$π^-)/Γ_{π^-}(_Λ^{3}$H) determined in helium bubble-chamber experiments, and adding $Γ_{π^0}(_Λ^{3}$H) through the $ΔI=\frac{1}{2}$ rule, we derive $τ(_Λ^{3}$H) assuming several different values of the $Λ$ separation energy $B_Λ(_Λ^{3}$H). It is concluded that each of ALICE and STAR reported $τ(_Λ^{3}$H) intervals implies its own constraint on $B_Λ(_Λ^{3}$H): $B_Λ\lesssim 0.1$ MeV for ALICE, $B_Λ\gtrsim 0.2$ MeV for STAR.

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A. Pérez-Obiol, D. Gazda, E. Friedman, A. Gal. 2020-12-04. Revisiting the hypertriton lifetime puzzle. https://doi.org/10.1016/j.physletb.2020.135916

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