Influence of terms on s- and p-shell contributions to the asymmetry parameter of Λp→np decay

Here is evaluated the effect of the isospin terms of weak interaction on the asymmetry parameter, aΛ, for proton induced nonmesonic hypernuclear weak decay, Λp→np. 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 isospin changes have been included through an adequate modification of the weak coupling constants. A comparison with contribution is made for s- and p-shell hypernuclei. It is analytically shown and numerically corroborated for 12ΛC and 5ΛHe that 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 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.