Lambda-nucleon Interaction Research Articles

Effective lambda-proton and lambda-neutron potentials from subthreshold inverse scattering

Potentials are constructed for the lambda-nucleon interaction in the and channels. These potentials are recovered from scattering phases below the inelastic threshold through Gel’fand-Levitan-Marchenko theory. Experimental data with good statistics is not available for lambda-nucleon scattering. This leaves theoretical scattering phases as the only option through which the rigorous theory of quantum inverse scattering can be used in probing the lambda-nucleon force. Using rational-function interpolations on the theoretical scattering data, the kernels of the Gel’fand-Levitan-Marchenko integral equation become degenerate, resulting in a closed-form solution. The new potentials restored, which are shown to be unique through the Levinson theorem, bear the expected features of short-range repulsion and intermediate-range attraction. Charge symmetry breaking, which is perceptible in the scattering phases, is preserved in the new potentials. The lambda-nucleon force in the channel is observed to be stronger than in the channel, as expected. In addition, the potentials bear certain distinctive features whose effects on hypernuclear systems can be explored through Schrödinger calculations.

A study of Λ hypernuclei within the Skyrme–Hartree–Fock model

We investigate the properties of the single Lambda hypernuclei within a Skyrme-Hartree-Fock (SHF) model. The parameters of the Skyrme type effective lambda-nucleon (Lambda N) interaction are obtained by fitting to the experimental Lambda binding energies of hypernuclei with masses spanning a wide range of the periodic table. Alternative parameter sets are also obtained by omitting nuclei below mass number 16 from the fitting procedure. The SHF calculations are performed for the binding energies of the Lambda single-particle states over a full mass range using the best fit parameter sets obtained in these fitting procedures and the results are compared with the available experimental data. The data show some sensitivity to the parameter sets obtained with or without including the nuclei below mass 16. The radii of the Lambda orbits in the hypernuclear ground states and the Lambda effective mass in nuclear matter show some dependence on different parameter sets. We present results for the total binding energy per baryon of the hypernuclei over a large mass region to elucidate their stability as a function of the baryon number. We have also employed the our best fit Lambda N parameter sets to investigate the role of hyperons in some key properties of neutron stars.

HYPERNUCLEI WITH A MICROSCOPIC LAMBDA-NUCLEON FORCE

We study properties of Λ hypernuclei in an extended Skyrme-Hartree-Fock model employing recent modern nucleonic Skyrme forces together with a microscopic lambda-nucleon interaction derived from Brueckner-Hartree-Fock calculations of hypernuclear matter with the Nijmegen soft-core hyperon-nucleon potentials. We show in particular recent results of deformed and neutron-rich hypernuclei close to the dripline.

Hypernuclei with a Microscopic Lambda-Nucleon Force

We study properties of Λ hypernuclei in an extended Skyrme-Hartree-Fock model employing recent modern nucleonic Skyrme forces together with a microscopic lambda-nucleon interaction derived from Brueckner-Hartree-Fock calculations of hypernuclear matter with the Nijmegen soft-core hyperon-nucleon potentials. We confront with experimental data on single-particle levels of single-Λ hypernuclei and bond energies of double-Λ hypernuclei, and present also recent results for deformed and neutron-rich hypernuclei close to the dripline.

Nonrelativistic mean-field description of the deformation of Λ hypernuclei

The deformations of light Λ hypernuclei are studied in an extended nonrelativistic deformed Skyrme-Hartree-Fock approach with realistic modern nucleonic Skyrme forces, pairing correlations, and a microscopical lambda-nucleon interaction derived from Brueckner-Hartree-Fock calculations. Compared to the large effect of an additional Λ particle on nuclear deformation in the light soft nuclei within relativistic mean field method, this effect is much smaller in the nonrelativistic mean-field approximation.

Properties of deformed Λ hypernuclei

The properties of Be and B isotopes and the corresponding Λ hypernuclei are studied by using a deformed Skyrme Hartree–Fock approach with realistic nucleonic Skyrme forces, pairing correlations, and a microscopically determined lambda-nucleon interaction based on Brueckner–Hartree–Fock calculations of hypernuclear matter. The results suggest that the core nuclei and the corresponding hypernuclei have similar deformations with the same sign.

Hypernuclei in the deformed Skyrme-Hartree-Fock approach

The properties of Lambda hypernuclei in a broad mass region are studied by using a deformed Hartree-Fock approach using realistic nucleonic Skyrme forces, pairing correlations, and a microscopically determined lambda-nucleon interaction based on Brueckner-Hartree-Fock calculations of hypernuclear matter. The results suggest that the core nuclei and the corresponding hypernuclei have similar deformations with the same sign. Some light single-Lambda hypernuclei are substantially deformed and the Lambda binding energy is modified by the deformation.

Hypernuclei in the Skyrme-Hartree-Fock formalism with a microscopic hyperon-nucleon force

We determine properties of single and multilambda hypernuclei in the Skyrme-Hartree-Fock formalism, which is supplemented by a microscopic in-medium lambda-nucleon interaction derived from self-consistent Brueckner-Hartree-Fock calculations with the Nijmegen soft-core hyperon-nucleon potential. Existing data for single-lambda hypernuclei are well reproduced, apart from a slight underbinding of heavy nuclei. In multilambda hypernuclei, we study in particular the effects of the modification of the nuclear core due to the presence of the hyperons.

Strangeness violating lambda-nucleon cross-section from hypernuclei life times

It is shown that the recently obtained hypernuclei life-times can be explained in term of a weak strangeness violating lambda-nucleon interaction with a cross section close to 6.0 10−15 barns.

Fission of heavy hypernuclei

The results on delayed and prompt fission of heavy hypernuclei obtained by the LEAR PS177 collaboration are recalled and discussed. It is shown that the hypernuclei life-times can be explained in term of a weak strangeness violating lambda-nucleon interaction with a cross section close to 6.0 10 −15 barns. The lambda attachment function is shown to be sensitive to the scission configuration, just before fission, and to the neck dynamics. This function provides a new way to study the nuclear scission process.

Phenomenological study of lambda-nucleon interaction

A joint fit has been made to the binding energy data of the $A=3\ensuremath{-}4$ hypernuclei (ground and excited states) together with the $\ensuremath{\Lambda}\ensuremath{-}p$ scattering data in order to deduce depth and range parameters of a phenomenological $\ensuremath{\Lambda}$-nucleon potential. Having determined the potential parameters we were able to infer the scattering lengths and effective ranges for the $\ensuremath{\Lambda}\ensuremath{-}p$ and $\ensuremath{\Lambda}\ensuremath{-}n$ systems.NUCLEAR REACTIONS $\ensuremath{\Lambda}$-nucleon potential inferred from the data; effective range parameters calculated.

New techniques advance hypernuclear spectroscopy

A feasible and fruitful way to study the spectroscopy of hypernuclei has been demonstrated by two experiments that applied counter techniques to measure hypernuclear reactions induced by K− mesons in flight. Such studies have been made possible in recent years by the development of intense, low‐momentum K− beams. They were further stimulated by the suggestions of theorists that production of hypernuclei by K− mesons in flight might favor the formation of states in which a nucleon of the parent nucleus is replaced by a lambda hyperon without otherwise changing the wave functions. Comparison of such a hypernuclear state with the corresponding nuclear state could yield useful information about the lambda–nucleon interaction.

Λ-Nucleon Charge-Symmetry-Breaking Interaction. I. Separable Potentials

The existence of a charge-symmetry-breaking (CSB) term in the lambda-nucleon ($\ensuremath{\Lambda}\ensuremath{-}N$) interaction is shown to produce an admixture of a $T=1$ state to the predominant isospin singlet state in $_{\ensuremath{\Lambda}}\mathrm{H}^{3}$. The present analysis shows that a CSB term constructed to fit light hypernuclear and $\ensuremath{\Lambda}\ensuremath{-}p$ scattering data is poorly determined (\ensuremath{\sim}4%-25% of the total $\ensuremath{\Lambda}\ensuremath{-}p$ singlet and \ensuremath{\sim}4%-15% of the total $\ensuremath{\Lambda}\ensuremath{-}p$ triplet interaction), but is strongly correlated with the $\ensuremath{\Lambda}$-separation energy, ${B}_{\ensuremath{\Lambda}}$, from $_{\ensuremath{\Lambda}}\mathrm{H}^{3}$, and that isospin mixing in $_{\ensuremath{\Lambda}}\mathrm{H}^{3}$ can lead to significant adjustments of the deduced $\ensuremath{\Lambda}\ensuremath{-}N$ interaction strengths. The mixed-symmetry $T=0$ state in $_{\ensuremath{\Lambda}}\mathrm{H}^{3}$ is seen to have a small effect. Data employed include $\ensuremath{\Lambda}\ensuremath{-}p$ total cross sections, $\ensuremath{\sigma}(\ensuremath{\Lambda}p)$, for total c.m. energy ${E}_{\mathrm{c}.\mathrm{m}.}<18$ MeV, published values of ${B}_{\ensuremath{\Lambda}}$, and a theoretical determination by Herndon and Tang of the relative magnitudes of the $\ensuremath{\Lambda}\ensuremath{-}N$ potentials responsible for the mean binding and the ground-state splitting of $_{\ensuremath{\Lambda}}\mathrm{He}^{4}$ and $_{\ensuremath{\Lambda}}\mathrm{H}^{4}$. The two hypotheses that the spin, $I$, of $_{\ensuremath{\Lambda}}\mathrm{He}^{4}$ is 0 and 1 are studied. Nonlocal separable, spin-dependent central interactions of the Yamaguchi form are used, and all range parameters in the $\ensuremath{\Lambda}\ensuremath{-}N$ interaction are constrained to be equal. A search of fits to $\ensuremath{\sigma}(\ensuremath{\Lambda}p)$ is made with intrinsic ranges in the interval 1.5 F to 2.3 F. Self-consistent CSB potentials are found for $I=0$ and $I=1$. The deduced singlet $\ensuremath{\Lambda}\ensuremath{-}p$ CSB interaction is attractive in all cases, in disagreement with predictions of the S${\mathrm{U}}_{3}$ particle-mixing model of Downs.

A-nucleon potential

Potentials to describe the hyperon-nucleon interaction have been calculated some time ago with the prescription of Brueckner and Watson. They treat the ∧ and Σ channels on equal footing. We have calculated from them an effective potential for the lambda-nucleon interaction that takes only implicity the effect of the closed Σ channel into account. This procedure, however, is not restricted to the hyperonnucleon case, although we only applied it there. The potentials we used were in accordance with an even ∧-Σ parity and with unitary symmetry for the pseudovector coupling constants, which they contain as parameters. It is shown that the phase shifts, resulting from the effective ∧N potential, coincide, up to about the threshold for Σ production, with the ones obtained from the original hyperon-nucleon potentials. Calculations were done both for the singlet and triplet cases. In this way, one gets an impression about the effective amounts of central, spin-orbit and tensor force in the ∧N interaction.

AverageΛ-Nucleon Interaction in the Hypertriton

Abstract : Upper bounds on the strength of the average lambdanucleon interaction required to account for the observed binding of the hypertriton have been established in a variation calculation with a ten-parameter trial function. Central two-body potentials having hard-core radii 0.2, 0.4, and 0.6 F and ranges suggested by consideration of the two-pion-exchange mechanism were used. These calculations led to improvements of 3-6% (depending upon the hard-core radius) in the required strengths over the results of previous calculations with a four-parameter function. The results cannot be used to rule out the existence of a bound hyperdeuteron of spin 0 for a hard-core radius as large as 0.6 F. A partial variation calculation is described, in which only two of the ten parameters of the trial function are varied. When the remaining parameters are fixed by consideration of the two-body subsystems of which the hypertriton is composed, variation of two appropriate parameters leads to required strengths within 3% of the values obtained by varying all ten parameters. (Author)