Delta T=3/2 contribution of pseudoscalar mesons to Lambda N -> NN observables within an independent particle shell-model framework

C. BARBERO

JOURNAL OF PHYSICS G. NUCLEAR PHYSICS

IOP Publishing

Año: 2007 vol. 34 p. 1971 - 1983

0305-4616

The effect of Delta T=3/2 isospin terms of weak interaction on the main nonmesonic hypernuclear weak decay observables, the total rate, Gamma_{NM}, the neutron-to-protonbranching ratio, Gamma_{n/p}, and the proton asymmetry parameter, a_Lambda, is evaluated. A general shell model formalism for finite hypernuclei recently developed has been used. A strangeness-changing weak Lambda N -> NN transition potential including the exchange of pseudoscalar mesons (pion, eta, K) is adopted. The effects of Delta T=3/2 isospin changes have been added through an adequate modification of the weak coupling constants and a comparison with Delta T=3/2 contribution is made, both for ^{12}_{Lambda}C and ^5_{Lambda}He. Numerical computations show that the effect on the decay rates is very small and the neutron to proton ratio is reduced in 4%. The asymmetry parameter a_Lambda is increased in the same percentage. We conclude that the effect of Delta T=3/2 terms helps to enhance a_Lambda value but diminishes Gamma_{n/p}, both in a few percent. In this regard, Delta T=3/2 contribution of pseudoscalar mesons is not enough to reproduce the experimental data. The necessity of a detailed analysis including vector meson exchange is suggested.