A Λ-hyperon, when placed in the nuclear medium, will be modified from its noninteracting form in much the same way as the nucleons themselves are altered by their mutual interactions. The same coupling between sp and two-particle-one-hole (2p1h) states that alters the Λ sp spectrum serves to move particle strength to high energy for a given momentum. The resulting spectral function calculated for a realistic hyperon-nucleon (YN) interaction ref.1 indicates that about 15% of the Λ strength is removed from the lowest states, compared to about 30% for a nucleon at the Fermi momentum in a similar calculation. A complete study of the Λ self-energy and spectral function in nuclear matter can be found in publ.98. The primary decay mode for the Λ particle in a dense nuclear medium is a non-mesonic ΛN-NN decay ref.2. Details of the YN weak interaction aside, this decay mechanism is sensitive to correlations in the initial YN state, to how the nucleon which "catalyzes" the decay is described, and to how the final-state nucleons are dressed in the medium and correlated with each other. Correlations between the YN pair differ among the important partial wave channels, and are not as strong as typically assumed. Our calculations suggest that the nonmesonic decay width increases accordingly with a more realistic treatment of correlations. We have also observed that the ΣN-NN decay channel is made important by the strong coupling between ΛN and ΣN states ref.3. As a result, the contribution to the decay from the strong conversion to the ΣN state prior to subsequent weak decay of the Σ increases the decay width substantially. A paper on this work has been published in publ.100. For even more details see the thesis of Neil Robertson that is available from here.
REFERENCES