Talks at the Workshop
The Coulomb breakup of oneneutron halo nuclei is
discussed as a method to study the singleparticle structure. Extracted
spectroscopic factors are compared to those deduced from nuclear oneneutron
removal reactions. Finally, an outlook is given on the nearfuture
experimental programme.
The dynamical eikonal approximation is a quantal method
unifying the semiclassical timedependent 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 ^{11}Be halo nucleus on ^{12}C and ^{208}Pb
near 70 MeV/nucleon, without any parameter adjustment. Elastic scattering of
^{11}Be on ^{12}C near 50 MeV/nucleon is well reproduced.
Parallel momentum distributions and differential cross section for the
elastic breakup of ^{8}B on ^{208}Pb 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 threebody 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 threebody model using realistic
binary interactions. General analytic properties of threebody scattering
and transition amplitudes as well as analysis of spatial correlations give
helpful unique signature of the threebody resonances. The intrinsic
correlated structures of the continuum reveal threebody 2^{+}_{1},
2^{+}_{2}, 1^{+}_{1} resonances in ^{6}He,
0^{+}_{1}, 0^{}_{1} resonant structure in
^{11}Li, and a lack of resonant structure in soft dipole and
monopole excitations in ^{6}He and in the ^{11}Li 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 neutronrich lithium isotopes.
Abstract:
Abstract:
Abstract:
I will discuss recent largescale ab initio studies of
exotic nuclei and halo states. The foundation of our approach is the ab
initio nocore shell model (NCSM), which is a wellestablished theoretical
framework aimed at an Abody description of nuclear structure starting from
highprecision 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 oneproton halo nucleus
^{8}B and the oneneutron halo nucleus ^{11}Be, as well as
the more normal ^{7}Be. 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 P_{1}+P_{2} A_{T}^{1/3}.
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 ^{7}Be.
We find further that we cannot ignore Coulombnuclear 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 ^{
11}Li and the inelastic scattering of ^{14}Be are presented.
These experiments were performed at RIKEN by applying the invariant mass
method at intermediate energies. In the Coulomb breakup of ^{11}Li
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 E_{rel} = 0 MeV made possible this
observation. The observed large E1 transitions suggests a strong
neutronneutron correlation in the halo. The peculiar twobody decay
correlations were also observed in ^{10}Li energy spectra, which may
suggest the important role of twobody interaction in the threebody system.
For ^{14}Be, we have observed the first 2^{+} state at 1.55
MeV with lower deformation length compared to the ^{12}Be. 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 ^{11}Be,
taken to be given as a neutron attached to a ^{10}Be core. The core
states are described by HFB and QRPA theory. States in ^{11}Be are
obtained in the Dynamical Core Polarization (DCP) theory as superposition of
one quasiparticle meanfield 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 ^{11}Be on protons,
^{9}Be and ^{208}Pb are presented and discussed.
The scattering of the Borromean nucleus ^{6}He 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 threebody projectile. The ContinuumDiscretized Coupled Channels (CDCC)
framework is used for the scattering calculations.
The Unitary Correlation Operator Method (UCOM) is an
efficient tool for the description of interactioninduced central and tensor
correlations. It provides a correlated interaction V_{UCOM}, which
is tamed with respect to the dominant shortrange correlations and requires
only minimal additional threenucleon forces to describe various nuclear
properties on a quantitative level. Applications within the nocore shell
model to pshell nuclei demonstrate that ground state energies and
excitation spectra are in good agreement with experiment. Even subtle
features usually viewed as a hallmark of threebody forces can be reproduced
with the V_{UCOM} twobody interaction alone.
Correlation studies in breakup reactions at relativistic
energies are presented. The Borromean systems  ^{6}He, ^{11}Li
and ^{14}Be  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 knockout and nuclear and coulomb inelastic scattering,
respectively. Ground state properties e.g. spectroscopic factors can be
extracted from the 1n data by reconstructing the centerofmass 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 twonucleon haloes are
now very well documented, but the more general implications of
paircorrelations, in e.g. very neutron rich systems, have yet to emerge or
assessed quantitatively. It is therefore of interest to investigate whether
twonucleon 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 twostep processes (onenucleon 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
threebody 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 selforganization 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.
