Influence of [formula omitted] terms on s- and p-shell contributions to the asymmetry parameter of [formula omitted] decay

Abstract

Here is evaluated the effect of the Δ T = 3 2 isospin terms of weak interaction on the asymmetry parameter, a Λ , for proton induced nonmesonic hypernuclear weak decay, Λ p → n p . There has been used a general shell model formalism for finite hypernuclei recently developed. A strangeness-changing weak transition potential including the exchange of pseudoscalar mesons ( π, η, K) is adopted. The effects of Δ T = 3 2 isospin changes have been included through an adequate modification of the weak coupling constants. A comparison with Δ T = 1 2 contribution is made for s- and p-shell hypernuclei. It is analytically shown and numerically corroborated for 12 Λ C and 5 Λ He that Δ T = 3 2 terms affect approximately in the same percentage both s- and p-shell contributions to proton asymmetry parameter. The value of this observable is increased in ∼ 4 % . The effect of Δ T = 3 2 terms helps to enhance the asymmetry parameter value, but is not enough to reproduce the experimental data. The necessity of a similar detailed analysis including vector meson exchange is suggested.