9 Exchange terms in the two – nucleon induced non – mesonic weak decay of Λ – hypernuclei

The contribution of Pauli exchange terms to the two–nucleon induced non–mesonic weak decay of 12 Λ C hypernuclei, ΛNN → nNN (N = n or p), is studied within a nuclear matter formalism implemented in a local density approximation. We have adopted a weak transition potential including the exchange of the complete octets of pseudoscalar and vector mesons as well as a residual strong interaction modeled on the Bonn potential. The introduction of exchange terms turns out to reduce the two–nucleon induced non–mesonic rate by 18% and, jointly with an increase in the one–nucleon induced rate by the same magnitude, reveals to be significant for an accurate determination of the full set of hypernuclear non–mesonic decay widths in theoretical and experimental analyses.