15,015 research outputs found
Spin-dependent effective interactions for halo nuclei
We discuss the spin-dependence of the effective two-body interactions
appropriate for three-body computations. The only reasonable choice seems to be
the fine and hyperfine interactions known for atomic electrons interacting with
the nucleus. One exception is the nucleon-nucleon interaction imposing a
different type of symmetry. We use the two-neutron halo nucleus 11Li as
illustration. We demonstrate that models with the wrong spin-dependence are
basically without predictive power. The Pauli forbidden core and valence states
must be consistently treated.Comment: TeX file, 6 pages, 3 postscript figure
Origin of Borromean systems
The complex energies of the three-body resonances for one infinitely heavy
particle and two non-interacting light particles are the sum of the two
contributing two-body complex resonance energies. The bound state of a
Borromean system originates from a resonance when the third interaction is
introduced, a finite mass is allowed and proper angular momentum coupling is
included. The relative importance of these contributions are investigated and
the resulting structure of Borromean systems are traced back to the two-body
continuum properties. The and states in He result from
neutron-core p-states and the ground and first excited state of Li
originate from neutron-core and -states.Comment: Physics Letters B, in pres
Resonances in three-body systems with short and long-range interactions
The complex scaling method permits calculations of few-body resonances with
the correct asymptotic behaviour using a simple box boundary condition at a
sufficiently large distance. This is also valid for systems involving more than
one charged particle. We first apply the method on two-body systems. Three-body
systems are then investigated by use of the (complex scaled) hyperspheric
adiabatic expansion method. The case of the 2 resonance in Be and
Li is considered. Radial wave functions are obtained showing the correct
asymptotic behaviour at intermediate values of the hyperradii, where wave
functions can be computed fully numerically.Comment: invited talk at the 18th International Conference on Few-Body
Problems in Physics, Santos-S.Paulo, August 21-26, 200
Isospin mixing and energy distributions in three-body decay
The structure of the second 2 resonance in Li is investigated with
special emphasis on its isospin 0 components. The wave functions are computed
in a three-body model (++) using the hyperspherical adiabatic
expansion method combined with complex scaling. In the decay into three free
particles the symmetry conserving short-range interaction dominates at short
distance whereas the symmetry breaking Coulomb interaction dominates at
intermediate and large distances resulting in substantial isospin mixing. We
predict the mixing and the energy distributions of the fragments after decay.
Computations are consistent with available experiments. We conjecture that
nuclear three-body decays frequently produce such large isospin mixing at large
distance where the energy distributions. are determined.Comment: 5 pages, 4 figures, to be published in Physics Letters
Breakup of three particles within the adiabatic expansion method
General expressions for the breakup cross sections in the lab frame for
reactions are given in terms of the hyperspherical adiabatic basis. The
three-body wave function is expanded in this basis and the corresponding
hyperradial functions are obtained by solving a set of second order
differential equations. The -matrix is computed by using two recently
derived integral relations. Even though the method is shown to be well suited
to describe processes, there are nevertheless particular configurations
in the breakup channel (for example those in which two particles move away
close to each other in a relative zero-energy state) that need a huge number of
basis states. This pathology manifests itself in the extremely slow convergence
of the breakup amplitude in terms of the hyperspherical harmonic basis used to
construct the adiabatic channels. To overcome this difficulty the breakup
amplitude is extracted from an integral relation as well. For the sake of
illustration, we consider neutron-deuteron scattering. The results are compared
to the available benchmark calculations
Momentum distributions and reaction mechanisms for breakup of two--neutron halos
A theoretical model able to describe fragmentation reactions of three--body
halo nuclei on different targets, from light to heavy, is used to compute
neutron and core momentum distributions. Both Coulomb and nuclear interactions
are simultaneously included. We specify the different reaction mechanisms
related to various processes. The method is applied to fragmentation of He
and Li on C and Pb. We find good agreement with the available
experimental results.Comment: 10 pages, 3 figures, Phys.Lett.B in pres
Recombination rates from potential models close to the unitary limit
We investigate universal behavior in the recombination rate of three bosons
close to threshold. Using the He-He system as a reference, we solve the
three-body Schr\"odinger equation above the dimer threshold for different
potentials having large values of the two-body scattering length . To this
aim we use the hyperspherical adiabatic expansion and we extract the -matrix
through the integral relations recently derived. The results are compared to
the universal form, , for
different values of and selected values of the three-body parameter
. A good agreement with the universal formula is obtained after
introducing a particular type of finite-range corrections, which have been
recently proposed by two of the authors in Ref.[1]. Furthermore, we analyze the
validity of the above formula in the description of a very different system:
neutron-neutron-proton recombination. Our analysis confirms the universal
character of the process in systems of very different scales having a large
two-body scattering length
Three-body structure of the low-lying Ne-states
The Borromean nucleus Ne (O) is investigated by using
the hyperspheric adiabatic expansion for a a three-body system. The measured
size of O and the low-lying resonances of F (O) are
first used as constraints to determine both central and spin-dependent two-body
interactions. Then, the ground state structure of Ne is found to be an
almost equal mixture of and proton-O relative states, the
two lowest excited states have about 80% of -mixed components, and for the
next two excited three-body states the proton-O relative s-states do not
contribute. The spatial extension is as in ordinary nuclei. The widths of the
resonances are estimated by the WKB transmission through the adiabatic
potentials and found in agreement with the established experimental limits. We
compare with experimental information and previous works.Comment: 29 pages, 7 postscript figures, to be published in Nuclear Physics
Inclusive quasielastic electron scattering on He: a probe of the halo structure
We investigate inclusive electron scattering reactions on two-neutron halo
nuclei in the quasielastic region. Expressions for the cross section and
structure functions are given assuming that the halo nucleus can be described
as a three-body system (). The method is applied to He. We
compute cross sections and structure functions, and investigate the kinematic
conditions for which the observables are determined either by -knockout
or by halo neutron-knockout. The optimal kinematical domain to disantangle the
momentum distributions of the various components of the three--body system ( MeV/c and MeV) are explored.Comment: 10 pages, 3 figures. Physics Letters B, in pres
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