arXiv subjects

A. S. Jensen

Publications and source records attributed to A. S. Jensen.

173 records · Page 10Linked to original sources

arXiv1997

The simplest ``strange'' three-body halo

The recently developed method to solve the Faddeev equations in coordinate space is used to study the weakly bound halo nucleus, the hypertriton (Lambda + n + p). The long distances are treated carefully to achieve convergence and high accuracy. We use several sets of two-body interactions which reproduce the deuteron properties and provide the low-energy Lambda-nucleon scattering data close to that of two of Nijmegen potentials. We show that the details of the potentials are unimportant unless the accuracy of the hypertriton binding energy is required to be better than 50 keV. We find that the most significant parameter of the Lambda-nucleon interaction, the singlet s-wave scattering length, must be within 10% of 1.85 fm, when the Lambda-separation energy from the deuteron is about 130 keV. Other details of the Lambda-nucleon interaction are less important for the hypertriton structure. The scattering length and effective range are computed for scattering of a Lambda-particle on a deuteron. The folding model reducing the three-body problem to a two-body problem is investigated in this context and found to be inadequate.

nucl-th↗

arXiv1996

The Three-Body Continuum Coulomb Problem and the 3$α$ Structure of $^{12}$C

We introduce an approach, based on the coordinate space Faddeev equations, to solve the quantum mechanical three-body Coulomb problem in the continuum. We apply the approach to compute measured properties of the first two $0^+$ levels in $^{12}$C, including the width of the excited level, in a 3$α$-particle model. We use the two-body interaction which reproduces the low energy $α$-$α$ scattering data and add a three-body force to account for the compound state admixture.

nucl-th↗

arXiv1996

New Observables in Break-up Reactions of Three-body Halos

Momentum distributions of particles from fast three-body halo fragmentation reactions with polarized beams and outgoing fragments are analyzed by use of the sudden approximation. The final state interaction between the two non-disturbed particles is considered. We first give a general and detailed description of the method. We introduce observable quantities that emphasize the two-body correlations in the initial three-body structure as well as in the final two-body system. Using neutron removal from 11Li as an example we investigate the dependence of the polarization observables on the properties of the low-lying resonances and virtual states of the 10Li subsystem. These observables are very sensitive to the l > 0-waves in the wave functions, and they provide detailed information on the resonance structure of the neutron-core subsystem.

nucl-th↗

arXiv1996

Square-well solution to the three-body problem

The angular part of the Faddeev equations is solved analytically for s-states for two-body square-well potentials. The results are, still analytically, generalized to arbitrary short-range potentials for both small and large distances. We consider systems with three identical bosons, three non-identical particles and two identical spin-1/2 fermions plus a third particle with arbitrary spin. The angular wave functions are in general linear combinations of trigonometric and exponential functions. The Efimov conditions are obtained at large distances. General properties and applications to arbitrary potentials are discussed. Gaussian potentials are used for illustrations. The results are useful for numerical calculations, where for example large distances can be treated analytically and matched to the numerical solutions at smaller distances. The saving is substantial.

nucl-th↗

arXiv1996

The Pauli principle in a three-body cluster model and the momentum distributions after fragmentation of 6He and 11Li

We investigate two simple prescriptions to account for the Pauli principle in a three-body cluster model employing a new method based on an adiabatic hyperspherical expansion to solve the Faddeev equations in coordinate space. The resulting wave functions are computed and compared. They are furthermore tested on halo nuclei by calculations of momentum distributions and invariant mass spectra arising after fragmentation of fast $^6$He and $^{11}$Li in collisions with light targets. The prescriptions are very accurate and the available measured quantities are remarkably well reproduced when final state interactions are included.

nucl-th↗

arXiv1996

Three-body Halos. IV. Momentum Distributions after Fragmentation

Momentum distributions of particles from nuclear break-up of fast three-body halos are calculated incorporating effects of final state interactions. The same two-body interactions between the particles are used to calculate both the ground state structure and the final state of the reaction processes. The ground state wave function reproduces size and energy of the halo nucleus. First we give a general and detailed description of the method. Then we investigate the effect of final state interactions in neutron removal and core break-up reactions for one- and two-dimensional momentum distributions. We compute specifically core and neutron momentum distributions from 11Li fragmentation and compare those with available experimental data. We conclude that 11Li must have a neutron-core relative state containing a p-state admixture of 20\%-30\%. The fragmentation data also strongly suggest that 10Li has an s-state at about 50 keV and a p-state around 500 keV.

nucl-th↗

arXiv1996

Three-Body Halo Fragmentation: Polarization effects

Momentum distributions of particles from nuclear break-up of fast three-body halos are calculated for polarized beam and outgoing fragments. These momentum distributions are combined in observable quantities which emphasize the two-body correlations in the initial three-body structure as well as in the final two-body system. Applying the formalism to 11Li we find a sensitive dependence on the p-wave content and on the position of the p-resonances in 10Li. Polarization experiments are then a new tool to study correlations in nuclear halos.

nucl-th↗

arXiv1996

Momentum Distributions of Particles from Three--Body Halo Fragmentation: Final State Interactions

Momentum distributions of particles from nuclear break-up of fast three-body halos are calculated consistently, and applied to $^{11}$Li. The same two-body interactions between the three particles are used to calculate the ground state structure and the final state of the reaction processes. We reproduce the available momentum distributions from $^{11}$Li fragmentation, together with the size and energy of $^{11}$Li, with a neutron-core relative state containing a $p$-state admixture of 20\%-30\%. The available fragmentation data strongly suggest an $s$-state in $^{10}$Li at about 50 keV, and indicate a $p$-state around 500 keV.

nucl-th↗

arXiv1995

Three-body halos. III. Effects of finite core-spin

We investigate effects of finite core-spin in two-neutron halos in the three-body model consisting of two neutrons and a core. The states in the neutron-core subsystem can then have an additional splitting due to the coupling of the neutron and core spins. The connection between the structure of the total system and the states of the neutron-core subsystem depends strongly on this spin splitting. However, the spatial structure is essentially unchanged. The neutron momentum distribution in a nuclear dissociation reaction will consist of a broad and a narrow distribution arising from the two spin split neutron-core virtual states. The large distance behavior is investigated and the conditions for the Efimov effect turn out to be more restrictive. The magnetic moment is equal to the core-value independent of spin splitting and energies of the neutron-core states. The excited states of opposite parity depend strongly on the spin splitting. The parameters in our numerical examples are chosen to be appropriate for $^{11}$Li and $^{19}$B.

nucl-th↗

arXiv1994

Three-Body Halos. II. from Two- to Three-Body Asymptotics

The large distance behavior of weakly bound three-body systems is investigated. The Schrödinger equation and the Faddeev equations are reformulated by an expansion in eigenfunctions of the angular part of a corresponding operator. The resulting coupled set of effective radial equations are then derived. Both two- and three-body asymptotic behavior are possible and their relative importance is studied for systems where subsystems may be bound. The system of two nucleons outside a core is studied numerically in detail and the character of possible halo structure is pointed out and investigated.

nucl-th↗

arXiv1994

Efimov States in Halo Nuclei

We investigate conditions for the occurrence of Efimov states in the recently discovered halo nuclei. These states could appear in systems, where one neutron is added to a pronounced one-neutron halo nucleus. Detailed calculations of the properties of the states are presented and promising candidates are discussed.

nucl-th↗