Sigma meson exchange-effect on non-mesonic hypernuclear weak decay observables

C. BARBERO, A. MARIANO

Physical Review C

The American Physical Society

Año: 2005 vol. 73 p. 243091 - 243095

We analyze the influence of  sigma  meson exchange on themain non-mesonic hypernuclear weak decay observables:Total rate NM, neutron-to-proton branching ratio n/p, and proton asymmetry parameter a. The sigma  meson exchange is added to the standard strangeness-changing weak LambdaN  to  NN  transition potential, which includes the exchange of the complete pseudoscalar and vector mesons octe. Using a shell model formalism, the sigma meson weak coupling constants are adjusted to reproduce the recent NM and n/p experimental data for 5He. Numerical results for the remaining observables of 5He and all the observables of 12C 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 the a values, which means that other improvements of the model must be explored to explain the puzzle posed by the experiments.