Role of deformation in the nonmesonic decay of light hypernuclei

We discuss the nonmesonic decay of deformed p-shell hypernuclei. The Nilsson model with angular momentum projection is employed in order to take into account the deformation effects. The nonmesonic decay rate and the intrinsic $\Lambda$ asymmetry parameter decrease as a function of the deformation parameter, while the ratio of the neutron- to proton-induced decay rates increases. We find that the deformation effects change these observables by about 10 % for $^9_{\Lambda}$Be from the spherical limit.Comment: RevTex, 17 pages, 3 ps figure

Recent results on the nonmesonic weak decay of hypernuclei within a one-meson-exchange model

We update our previous results for the nonmesonic decay of $^{12}_\Lambda$C and $^5_\Lambda$He. We pay special attention to the role played by Final State Intreractions on the decay observables. We follow a One-Meson-Exchange model which includes the exchange of the $\pi, \rho, K, K^*, \eta$ and $\omega$ mesons. We also present recent predictions for different observables concerning the decay of the doubly strange $^6_{\Lambda \Lambda}$He hypernucleus.Comment: 4 pages. Contribution to the Mesons and Light Nuclei'01 Conference, Prague, 2-6 July 200

Lowest Order Effective Field Theory for the weak ΛN\Lambda N interaction

The $|\Delta S|=1$ $\Lambda N$ interaction, responsible for the decay of hypernuclei, is studied by means of an Effective Field Theory where the long range physics is described by pion and kaon exchange mechanisms, and its short range counterpart is obtained from the most general non-derivative local four-fermion interaction. We show that, including the Lowest Order Parity Conserving contact terms, allows us to reproduce the total decay rates for $^5_\Lambda {\rm He}$, $^{11}_\Lambda {\rm B}$ and $^{12}_\Lambda {\rm C}$ with a reasonable value of ${\hat \chi^2}$, while in order to get a prediction for the Parity Violating (PV) asymmetry compatible with experiments, we have to include the Lowest Order PV contact pieces.Comment: 3 pages, no figures. Contribution to the 17th International IUPAP Conference on Few-body Problems in Physics, June 5-10, 2003 Durham, North Carolina, USA. Uses espcrc1.st

Dynamical meson-baryon resonances with chiral Lagrangians

The s-wave meson-baryon interaction is studied using the lowest-order chiral Lagrangian in a unitary coupled-channels Bethe-Salpeter equation. In the strangeness $S=-1$ sector the low-energy $K^- p$ dynamics leads to the dynamical generation of the $\Lambda(1405)$ as a ${\bar K}N$ state, along with a good description of the $K^- p$ scattering observables. At higher energies, the $\Lambda(1670)$ is also found to be generated dynamically as a $K \Xi$ quasibound state for the first time. For strangeness S=0, it is the $S_{11}(1535)$ resonance that emerges from the coupled-channels equations, leading to a satisfactory description of meson-baryon scattering observables in the energy region around the $S_{11}(1535)$. We speculate on the possible dynamical generation of $\Xi$ resonances within the chiral $S=-2$ sector as ${\bar K} \Lambda$ or ${\bar K} \Sigma$ quasibound states.Comment: 8 pages, 5 figures, Talk given at NSTAR2001, Workshop on the Physics of Excited Nucleons, Mainz (Germany), March 7-10, to be published in World Scientifi

Violation of the Δ\DeltaI=1/2 rule in the nonmesonic weak decay of Λ\Lambda hypernuclei

Violations of the $\Delta$I=1/2 rule are investigated in the nonmesonic weak hypernuclear decay using a weak $\Lambda$N$\to$NN transition potential based on meson exchange. While the weak $\Delta$I=3/2 matrix elements of baryons with pseudoscalar mesons are known to be very small, the same matrix elements of baryons with vector mesons, evaluated in the factorization approximation, are found to be significant. Within the uncertainties of the factorization approximation we find that the total rate increases by at most 6% lying within the error bars of the more recent experimental result. The neutron- to proton-induced rate, on the other hand, can change by up to a factor of two, while the asymmetry parameter is strongly affected as well.Comment: 17 pages. Paper related to a contribution presented at the International Conference on Hypernuclear and Strange Particle Physics (HYP97). Submitted to Phys. Lett.

Light nuclei and hypernuclei from quantum chromodynamics in the limit of SU(3) flavor symmetry

The binding energies of a range of nuclei and hypernuclei with atomic number A \u3c = 4 and strangeness vertical bar s vertical bar \u3c = 2, including the deuteron, dineutron, H - dibaryon, He - 3, He - 3 (Lambda), He - 4, He - 4(Lambda), and He - 4(Lambda Lambda), are calculated in the limit of flavor - SU (3) symmetry at the physical strange-quark mass with quantum chromodynamics (without electromagnetic interactions). The nuclear states are extracted from lattice QCD calculations performed with n (f) = 3 dynamical light quarks using an isotropic clover discretization of the quark action in three lattice volumes of spatial extent L similar to 3.4 fm, 4.5 fm, and 6.7 fm, and with a single lattice spacing b similar to 0.145 fm. DOI: 10.1103/PhysRevD.87.03450

Deuteron and exotic two-body bound states from lattice QCD

Results of a high-statistics, multivolume lattice QCD exploration of the deuteron, the dineutron, the H-dibaryon, and the Xi(-)Xi(-) system at a pion mass of m(pi) similar to 390 MeV are presented. Calculations were performed with an anisotropic n(f) = 2 + 1 clover discretization in four lattice volumes of spatial extent L similar to 2.0, 2.5, 2.9, and 3.9 fm, with a lattice spacing of b(s) similar to 0.123 fm in the spatial direction and b(t) similar to b(s)/3.5 in the time direction. Using the results obtained in the largest two volumes, the Xi(-)Xi(-) is found to be bound by B(Xi-Xi-)0 = 14.0(1.4)(6.7) MeV, consistent with expectations based upon phenomenological models and low-energy effective field theories constrained by nucleon-nucleon and hyperon-nucleon scattering data at the physical light-quark masses. Further, we find that the deuteron and the dineutron have binding energies of B-d = 11(05)(12) MeV and B-nn = 7.1(5.2)(7.3) MeV, respectively. With an increased number of measurements and a refined analysis, the binding energy of the H-dibaryon is B-H = 13.2(1.8)(4.0) MeV at this pion mass, updating our previous result