Talks at the Workshop
The Coulomb breakup of one-neutron halo nuclei is
discussed as a method to study the single-particle structure. Extracted
spectroscopic factors are compared to those deduced from nuclear one-neutron
removal reactions. Finally, an outlook is given on the near-future
experimental programme.
The dynamical eikonal approximation is a quantal method
unifying the semi-classical time-dependent and eikonal methods by taking
into account interference effects. Two variants of the method can be
defined, differing by a phase choice. The 'coherent' variant respects
the rotational symmetry around the beam axis. Expressions are given for
different breakup cross sections. A good agreement is obtained with
experimental differential and integrated cross sections for the elastic
breakup of the 11Be halo nucleus on 12C and 208Pb
near 70 MeV/nucleon, without any parameter adjustment. Elastic scattering of
11Be on 12C near 50 MeV/nucleon is well reproduced.
Parallel momentum distributions and differential cross section for the
elastic breakup of 8B on 208Pb are also compared with
experiment.
Abstract:
The sensitivity of breakup calculations to the projectile
description is analysed. It is shown that breakup is influenced only by the
asymptotic properties of the nucleus model, namely the asymptotic
normalisation coefficient of the initial bound state, and the phase shifts
in the continuum.
Abstract:
General properties of the ground and three-body scattering
states of hundred thousand six hundred those folks so Boston is since this
is a sense is Norton's four and one +n+n three-body model using realistic
binary interactions. General analytic properties of three-body scattering
and transition amplitudes as well as analysis of spatial correlations give
helpful unique signature of the three-body resonances. The intrinsic
correlated structures of the continuum reveal three-body 2+1,
2+2, 1+1 resonances in 6He,
0+1, 0-1 resonant structure in
11Li, and a lack of resonant structure in soft dipole and
monopole excitations in 6He and in the 11Li dipole
response.
The availability of very intense, low emittance beams of
radioactive nuclei at low energy makes TRIUMF's ISAC facility one of the
best places in the world to study transfer reactions with halo nuclei. In
this talk I describe some of the experiments performed and planned this year
at ISAC with beams of neutron-rich lithium isotopes.
Abstract:
Abstract:
Abstract:
I will discuss recent large-scale ab initio studies of
exotic nuclei and halo states. The foundation of our approach is the ab
initio no-core shell model (NCSM), which is a well-established theoretical
framework aimed at an A-body description of nuclear structure starting from
high-precision interactions between the nucleons.
The dissociation of halo nuclei through their
collision with light and heavy targets is considered within the Continuum
Discretized Coupled Channels theory. We study the one-proton halo nucleus
8B and the one-neutron halo nucleus 11Be, as well as
the more normal 7Be. The procedure previously employed to extract
the Coulomb dissociation cross section by subtracting the nuclear one is
critically assessed, and the scaling law usually assumed for the target mass
dependence of the nuclear breakup cross section is also tested. It is found
that the nuclear breakup cross section for these very loosely bound nuclei
does indeed behave as P1+P2 AT1/3.
However, it does not have the geometrically inspired, Serber, form of a
circular ring which seems to be the case for normal nuclei such as 7Be.
We find further that we cannot ignore Coulomb-nuclear interference effects,
which may be constructive or destructive in nature, and so the errors in
previously extracted B(E1) using the subtraction procedure are almost
certainly underestimated. s
Abstract:
Recent experimental results on the Coulomb breakup of
11Li and the inelastic scattering of 14Be are presented.
These experiments were performed at RIKEN by applying the invariant mass
method at intermediate energies. In the Coulomb breakup of 11Li
we have observed a strong E1 transition at very low relative energies, which
were missing in the previous measurements. The high sensitivity of the
experimental setup down to Erel = 0 MeV made possible this
observation. The observed large E1 transitions suggests a strong
neutron-neutron correlation in the halo. The peculiar two-body decay
correlations were also observed in 10Li energy spectra, which may
suggest the important role of two-body interaction in the three-body system.
For 14Be, we have observed the first 2+ state at 1.55
MeV with lower deformation length compared to the 12Be. These
experimental results certainly need more theoretical works to understand the
Borromean halo properties. [1] T.Nakamura et al., Phys. Rev. Lett. 96,
252502 (2006)
Abstract:
The evolution of shell structures under the influence of
dynamical correlations is studied in the single neutron halo nucleus 11Be,
taken to be given as a neutron attached to a 10Be core. The core
states are described by HFB and QRPA theory. States in 11Be are
obtained in the Dynamical Core Polarization (DCP) theory as superposition of
one quasiparticle mean-field states and three quasiparticle core excited
configurations. Experimental signatures of the dynamical correlations of a
core with a single particle neutron have been compared with theoretical
calculations.
A model for breakup with core excitation of the projectile
is developed, as an extension of the Continuum discretized coupled channels
method (XCDCC). First results for the breakup of 11Be on protons,
9Be and 208Pb are presented and discussed.
The scattering of the Borromean nucleus 6He by
different targets and at differents energies is studied. A Transformed
Harmonic Oscillator (THO) basis is introduced to provide an appropriate
discrete and finite basis for treating the continuum part of the spectrum of
a three-body projectile. The Continuum-Discretized Coupled Channels (CDCC)
framework is used for the scattering calculations.
The Unitary Correlation Operator Method (UCOM) is an
efficient tool for the description of interaction-induced central and tensor
correlations. It provides a correlated interaction VUCOM, which
is tamed with respect to the dominant short-range correlations and requires
only minimal additional three-nucleon forces to describe various nuclear
properties on a quantitative level. Applications within the no-core shell
model to p-shell nuclei demonstrate that ground state energies and
excitation spectra are in good agreement with experiment. Even subtle
features usually viewed as a hallmark of three-body forces can be reproduced
with the VUCOM two-body interaction alone.
Correlation studies in breakup reactions at relativistic
energies are presented. The Borromean systems - 6He, 11Li
and 14Be - interact predominantly via nuclear or electromagnetic
processes depending on the target choice. A kinematically complete setup is
used in order to determine the full kinematics of the two and three body
final states in 1n knock-out and nuclear and coulomb inelastic scattering,
respectively. Ground state properties e.g. spectroscopic factors can be
extracted from the 1n data by reconstructing the center-of-mass motion of
the intermediate unbound system. The continuum structure is explored using
the inelastic scattering data. All analysis is done in Jacobi coordinates
giving access to angular correlations and energy sharing of the subsystems
in a natural way.
The importance of correlations in two-nucleon haloes are
now very well documented, but the more general implications of
pair-correlations, in e.g. very neutron rich systems, have yet to emerge or
assessed quantitatively. It is therefore of interest to investigate whether
two-nucleon removal might be used as a probe of such effects. In removal of
nucleons of the excess species, the reaction will not be direct and will
also receive contributions from two-step processes (one-nucleon removal plus
evaporation). This talk discusses such effects, especially the extent to
which we can calculate the direct component of such processes accurately. To
do so we make comparisons of sudden reaction theory methods with several
recent measurements, in test cases where both the structure is well
determined and the reaction is restricted energetically (by removal of a
nucleon pair of the deficient species) to be direct. The results are very
consistent across a range of systems.
Two decades have elapsed since the discovery of nuclear
halos by Tanihata and his team at Berkeley. The field has been driven by
remarkable experimental progress and discoveries, and more is to come with
new and upgraded facilities, like FAIR here in Europe. From finding adequate
phenomenological ways to describe the physics of the halo ground state,
ambitions have grown to also understand the halo continuum, also for
three-body Borromean halos. Theory has gradually become a useful partner for
experiment, also concerning predictions, although reaction theory remains a
challenge, in particular at lower energies, as has been demonstrated during
this workshop. This has however not prevented theory from having ambitions
to go further, to also understand the self-organization of halo systems in
an ab initio manner, i.e. starting out from nucleon constituents and
their interactions. This contributions is a reminder on how the road has
been made along the way - while we go.
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