π^- decay rates of p-shell hypernuclei revisited

Explicit expressions for the parity-violating s-wave and the parity-conserving p-wave contributions to π^- weak decay rates of Λ hypernuclei in the 1p shell are given in the weak-coupling limit, to update previous shell-model calculations and to compare with recent π^- spectra and total decay rates measured by the FINUDA Collaboration for _Λ⁷Li, _Λ⁹Be, _Λ¹¹B and _Λ¹⁵N. A useful sum rule for the summed strength of Λ_{1 s} → p_{1 p} hypernuclear π^- weak decays is derived. Fair agreement between experiment and calculations is reached, using the primary s-wave amplitude and Cohen-Kurath nuclear wavefunctions. The role of the p-wave amplitude is studied in detail for _Λ¹⁵N and found to be secondary. Previous assignments of ground-state spin-parity values J^π (_Λ⁷Li_g.s.) = frac(1, 2)⁺ and J^π (_Λ¹¹B_g.s.) = frac(5, 2)⁺ are confirmed, and a new assignment J^π (_Λ¹⁵N_g.s.) = frac(3, 2)⁺ is made, based on the substantial suppression calculated here for the _Λ¹⁵N (frac(1, 2)⁺) → π^{- 15}O_g.s. weak decay rate.