Revisiting the hypertriton lifetime puzzle

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 the STAR Collaboration's reported range of τ( Λ 3 H) values is considerably shorter: τ STAR ( Λ 3 H)∼(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 → 3 He + π − ). Significant but opposing contributions arise from ΣNN admixtures in Λ 3 H and from π − -3He distorted waves. Evaluating the inclusive π − decay rate Γ π − ( Λ 3 H) via a branching ratio Γ( Λ 3 H → 3 He+ π − ) / Γ π − ( Λ 3 H) determined in helium bubble-chamber experiments, and adding Γ π 0 ( Λ 3 H) through the Δ I = 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 ≲ 0.1 MeV for ALICE, B Λ ≳ 0.2 MeV for STAR.