sigma meson exchange effect on nonmesonic hypernuclear decay observables

C. BARBERO Y A. MARIANO

Physical Review C

American Physical Society

Año: 2006 vol. 73 p. 243091 - 243095

0556-2813

We analyze the influence of $sigma$ meson exchange on the main nonmesonic hypernuclear weak decay observables: the total rate,$Gamma_{NM}$, the neutron-to-proton branching ratio, $Gamma_{n/p}$, and the proton asymmetry parameter, $a_Lambda$. The $sigma$ meson exchange is added to the standard strangeness-changing weak $Lambda N ightarrow NN$ transition potential, which includes the exchange of the complete pseudoscalar and vector mesons octet ($pi$, $eta$, $K$, $ ho$, $omega$, $K^*$). Using a shell model formalism, the $sigma$ meson weak coupling constants are adjusted to reproduce the recent $Gamma_{NM}$ and $Gamma_{n/p}$ experimental data for $^5_{Lambda}He$. Numerical results for the remaining observables of $^5_{Lambda}He$ and all the observables of $^{12}_{Lambda}C$ decays are presented. They clearly show that the addition of the $sigma$ meson improves the agreement with the data. However, its effect it is not enough to reproduce well $a_Lambda$ values, which means that another improvements of the model must be explored to explain the puzzle posed by the experiments.