Formula omitted] decay rates of p-shell hypernuclei revisited

Abstract

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 1 p 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 Li Λ 7 , Be Λ 9 , B Λ 11 and N Λ 15 . 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 N Λ 15 and found to be secondary. Previous assignments of ground-state spin-parity values J π ( Li g.s. Λ 7 ) = 1 2 + and J π ( B g.s. Λ 11 ) = 5 2 + are confirmed, and a new assignment J π ( N g.s. Λ 15 ) = 3 2 + is made, based on the substantial suppression calculated here for the N Λ 15 ( 1 2 + ) → π − O g.s. 15 weak decay rate.