Role of ground-state correlations in hypernuclear nonmesonic weak decay

The contribution of ground-state correlations (GSCs) to the nonmesonic weak decay of _Λ¹²C and other medium to heavy hypernuclei is studied within a nuclear-matter formalism implemented in a local-density approximation. We adopt a weak transition potential including the exchange of the complete octets of pseudoscalar and vector mesons, as well as a residual strong interaction modeled on the Bonn potential. Leading GSC contributions, at first order in the residual strong interaction, are introduced on the same footing for all isospin channels of one- and two-nucleon induced decays. Together with fermion antisymmetrization, GSCs turn out to be important for an accurate determination of the decay widths. Besides opening the two-nucleon stimulated decay channels, for _Λ¹²C GSCs are responsible for 14% of the rate Γ₁ while increasing the Γₙ/Γₚ ratio by $4%$. Our final results for _Λ¹²C are ΓNM=0.98, Γₙ/Γₚ=0.34, and Γ₂/ΓNM=0.26. The saturation property of ΓNM with increasing hypernuclear mass number is clearly observed. The agreement with data of our predictions for ΓNM, Γₙ/Γₚ, and Γ₂ is rather good.