arXiv subjects

A. Cobis

Publications and source records attributed to A. Cobis.

5 recordsLinked to original sources

arXiv1998

Three-body halos. V. Computations of continuum spectra for Borromean nuclei

We solve the coordinate space Faddeev equations in the continuum. We employ hyperspherical coordinates and provide analytical expressions allowing easy computation of the effective potentials at distances much larger than the ranges of the interactions where only s-waves in the different Jacobi coordinates couple. Realistic computations are carried out for the Borromean halo nuclei 6He (n+n+α) for Jπ= 0+-, 1+-, 2+- and 11Li (n+n+9Li) for (1/2)+-, (3/2)+-, (5/2)+-. Ground state properties, strength functions, Coulomb dissociation cross sections, phase shifts, complex S-matrix poles are computed and compared to available experimental data. We find enhancements of the strength functions at low energies and a number of low-lying S-matrix poles.

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arXiv1998

Comment on "New modes of halo excitations in the 6He nucleus"

We try to explain the differences in the 6He dipole strength function in refs. [1] and [2]. We perform the full basis calculation of the strength function with the same renormalized interaction as in [1] and show that the size of the basis, needed for converged calculations of the 6He continuum spectrum, is much larger than that for the discrete spectrum. The renormalized interaction of [1] therefore cannot be used for the continuum spectrum calculations with the same basis as for the ground state.

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arXiv1997

Computations of Three-Body Continuum Spectra

We formulate a method to solve the coordinate space Faddeev equations for positive energies. The method employs hyperspherical coordinates and analytical expressions for the effective potentials at large distances. Realistic computations of the parameters of the resonances and the strength functions are carried out for the Borromean halo nucleus 6He (n+n+alpha) for J = 0+, 0-, 1+, 1-, 2+,2-. PACS numbers: 21.45.+v, 11.80.Jy, 31.15.Ja, 21.60.Gx

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arXiv1997

The Continuum Structure of the Borromean Halo Nucleus 11Li

We solve the Faddeev equations for 11Li (n+n+9Li) using hyperspherical coordinates and analytical expressions for distances much larger than the effective ranges of the interactions. The lowest resonances are found at 0.65 MeV (1/2+, 3/2+, 5/2+) and 0.89 MeV (3/2+, 3/2-) with widths of about 0.35 MeV. A number of higher-lying broader resonances are also obtained and related to the Efimov effect. The dipole strength function and the Coulomb dissociation cross section are also calculated. PACS numbers: 21.45.+v, 11.80.Jy, 21.60.Gx

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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.

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