Lifetime of the hypertriton

¹ Nuclear Physics Institute, 25068 Řež, Czech Republic
² Barcelona Supercomputing Center, 08034 Barcelona, Spain
³ Racah Institute of Physics, The Hebrew University, Jerusalem 91904, Israel

^* e-mail: gazda@ujf.cas.cz

Published online: 9 November 2022

Abstract

Conflicting values of the hypertriton lifetime τ(³_ΛH) 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 τ(³_ΛH) comes sufficiently close to the free-Λ lifetime τ_Λ, as expected naively for a very weakly bound Λ in ³_ΛH. We revisited theoretically this ³_ΛH lifetime puzzle [1], using ³_ΛH and ³He wave functions computed within the ab initio no-core shell model employing interactions derived from chiral effective field theory to calculate the two-body decay rate Γ(³_ΛH → ³He + π⁻). We found significant but opposing contributions arising from ΣNN admixtures in ³_ΛH and from π⁻ − ³He final-state interaction. To derive τ(³_ΛH), we evaluated the inclusive π⁻ decay rate Γ_π⁻ (³_ΛH) by using the measured branching ratio Γ(³_ΛH → ³He + π⁻)/Γ_π⁻ (³_ΛH) and added the π⁰ contributions through the ΔI = 1/2rule. The resulting τ(³_ΛH) varies strongly with the rather poorly known Λ separation energy E_sep(³_ΛH) and it is thus possible to associate each one of the distinct RHI τ(³_ΛH) measurements with its own underlying value of E_sep(³_ΛH).