ΛN\Lambda N correlations from the stopped K−K^- reaction on 4{}^4He

We have investigated correlations of coincident $\Lambda N$ pairs from the stopped $K^-$ reaction on ${}^4$He, and clearly observed $\Lambda p$ and $\Lambda n$ branches of the two-nucleon absorption process in the $\Lambda N$ invariant mass spectra. In addition, non-mesonic reaction channels, which indicate possible exotic signals for the formation of strange multibaryon states, have been identified.Comment: 5 pages, 3 figures, submitted to Physical Review Letter

Spin observables in the pn→pΛpn \to p \Lambda reaction

The T matrix of the LambdaN-> NN reaction, which is a strangeness changing weak process, is derived. The explicit formulas of the spin observables are given for s-wave p-Lambda final states which kinematically corresponds to inverse reaction of the weak nonmesonic decay of Lambda hypernuclei. One can study interferences between amplitudes of parity- conserving and violating, spin- singlet and triplet and isospin- singlet and triplet. Most of them are not available in the study of the nonmesonic decay. They clarify structure of the reaction and constrain strongly theoretical models for weak hyperon nucleon interaction.Comment: 7pages,ReVTeX,no figure

Nonmesonic Hyperon Weak Decay Spectra in Λ12^{12}_{\Lambda}C}

We study the nonmesonic weak decay (NMWD) $\Lambda N \to nN$ of the ${}^{12}_{\Lambda} C$ hypernucleus induced by the nucleon $N=n,p$ with transition rate $\Gamma_N$. The nuclear process is described by the interplay of two models; one describing the NMWD of hyperon $\Lambda$ in the nuclear environment, and the other taking into account the Final State Interaction (FSI) of the two outgoing nucleons with the residual nucleus. The first one is done in the framework of the Independent-Particle Shell-Model (IPSM), with the decay dynamics represented by the exchange of $\pi+ \eta+ K+\rho+\omega+K^*$ mesons with usual parametrization. For the second one is used a time dependent multicollisional intranuclear cascade schema (implemented in the CRISP code - Collaboration Rio-S\~ao Paulo). The results obtained for inclusive and exclusive kinetic energy spectra, and the angular correlation are compared with recent data from KEK and FINUDA experiments. The calculated ratio $(\Gamma_n / \Gamma_p)^{\partial{\tiny FSI}}$, between the numbers of emitted back-to-back $nn$ and $np$ pairs, is in good agreement with the experimental data.Comment: Proceedings of the International Nuclear Physics Conference 2010, Vancouver, BC - Canada 4-9 Jul 201