Perturbative QCD and weak asymmetries in lepton pair production: David J. E. Callaway. Department of Physics, FM-15, University of Washington, Seattle, Washington 98195.

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 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 LiΛ7, BeΛ9, BΛ11 and NΛ15. A useful sum rule for the summed strength of Λ1s→p1p 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 NΛ15 and found to be secondary. Previous assignments of ground-state spin-parity values Jπ(Lig.s.Λ7)=12+ and Jπ(Bg.s.Λ11)=52+ are confirmed, and a new assignment Jπ(Ng.s.Λ15)=32+ is made, based on the substantial suppression calculated here for the NΛ15(12+)→π−Og.s.15 weak decay rate.