S-wave approximation for asymmetry in nonmesonic decay of finite hypernuclei

We establish the bridge between the commonly used Nabetani-Ogaito-Sato- Kishimoto (NOSK) formula for the asymmetry parameter aΛ in the Λ→p→np emission of polarized hypernuclei, and the shell-model (SM) formalism for finite hypernuclei. We demonstrate that the s-wave approximation leads to a SM formula for aΛ that is as simple as the NOSK one and that reproduces the exact results for Λ5He and Λ12C better than initially expected. The simplicity achieved here is indeed remarkable. The new formalism makes the theoretical evaluation of aΛ more transparent and explains clearly why the one-meson exchange model is unable to account for the experimental data of Λ5He. © 2007 The American Physical Society.