Hypernuclear potentials and the pseudoscalar meson exchange contribution

The pieces of the hypernuclear strangeness violating potential due to the pseudoscalar meson exchanges are derived using methods which were successfully applied to hyperon nonleptonic decays. The estimates are tested by comparison with measured hyperon nonleptonic decay amplitudes. All isospin changes $\Delta I=1/2$ and $\Delta I=3/2$ are included in the derived potential. All calculational methods used are reviewed and described in detail

Hypernuclear potentials and the pseudoscalar meson exchange contribution

The pieces of the hypernuclear strangeness violating potential due to the pseudoscalar meson exchanges are derived using methods which were successfully applied to hyperon nonleptonic decays. The estimates are tested by comparison with measured hyperon nonleptonic decay amplitudes. All isospin changes ∆I = 1/2 and ∆I = 3/2 are included in the derived potential. All computational methods used are reviewed and described in detail

One-nucleon-induced nonmesonic hypernuclear decay in laboratory coordinates

We present a formalism for the computation of one-nucleon-induced nonmesonic weak hypernuclear decay rates in laboratory coordinates, within an independent-particle shell model framework, with a view to its generalization to the case of two-nucleon-induced transitions.Fil: Galeão, A. P.. Universidade Estadual Paulista Julio de Mesquita Filho. Instituto de Física Teórica; BrasilFil: Barbero, Cesar Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Física La Plata; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Exactas; ArgentinaFil: de Conti, C.. Universidade Estadual Paulista Julio de Mesquita Filho. Campus Experimental de Itapeva; BrasilFil: Krmpotic, Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Física La Plata; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentin

Weak meson vertices and the hypernuclear potential

This paper is a continuation of an earlier paper on hypernuclear potentials. A novel derivation of the hypernuclear strangeness-violating potential due to the pseudoscalar meson exchanges is presented. Comparison with the earlier method shows that the theoretical uncertainty is less than 30%. Relative signs of pseudoscalar meson exchanges and vector (axial vector) exchanges are discussed in detail. Additional comments on the nonrelativistic approximation are included

Kinetic energy sum spectra in nonmesonic weak decay of hypernuclei

We evaluate the coincidence spectra in the nonmesonic weak decay (NMWD) \Lambda N\go nN of $\Lambda$ hypernuclei $^{4}_\Lambda$He, $^{5}_\Lambda$He, $^{12}_\Lambda$C, $^{16}_\Lambda$O, and $^{28}_\Lambda$Si, as a function of the sum of kinetic energies $E_{nN}=E_n+E_N$ for $N=n,p$. The strangeness-changing transition potential is described by the one-meson-exchange model, with commonly used parameterization. Two versions of the Independent-Particle Shell Model (IPSM) are employed to account for the nuclear structure of the final residual nuclei. They are: (a) IPSM-a, where no correlation, except for the Pauli principle, is taken into account, and (b) IPSM-b, where the highly excited hole states are considered to be quasi-stationary and are described by Breit-Wigner distributions, whose widths are estimated from the experimental data. All $np$ and $nn$ spectra exhibit a series of peaks in the energy interval 110 MeV $<E_{nN}<170$ MeV, one for each occupied shell-model state. The IPSM-a could be a pretty fair approximation for the light $^{4}_\Lambda$He and $^{5}_\Lambda$He hypernuclei. For the remaining, heavier, hypernuclei it is very important, however, to take into account the spreading in strength of the deep-hole states, and bring into play the IPSM-b approach. Notwithstanding the nuclear model that is employed the results depend only very weakly on the details of the dynamics involved in the decay process proper. We propose that the IPSM is the appropriate lowest-order approximation for the theoretical calculations of the of kinetic energy sum spectra in the NMWD. It is in comparison to this picture that one should appraise the effects of the final state interactions and of the two-nucleon-induced decay mode.Comment: v1: 20 pages, 3 figures, 1 table, submitted for publication; v2: minor corrections, improved figures, published versio

s-Wave Approximation for Asymmetry in Nonmesonic Decay of Finite Hypernuclei

We establish the bridge between the commonly used Nabetani-Ogaito-Sato-Kishimoto (NOSK) formula for the asymmetry parameter $a_\Lambda$ in the $\vec\Lambda p \to np$ emission of polarized hypernuclei, and the shell model (SM) formalism for finite hypernuclei. We demonstrate that the s-wave approximation leads to a SM formula for $a_\Lambda$ that is as simple as the NOSK one, and that reproduces the exact results for $^5_\Lambda$He and $^{12}_\Lambda$C better than initially expected. The simplicity achieved here is indeed remarkable. The new formalism makes the theoretical evaluation of $a_\Lambda$ more transparent, and explains clearly why the one-meson exchange model is unable to account for the experimental data of $^5_\Lambda$He.Comment: 9 pages. to be published in Physical Review