Workshop: The Physics of Halo Nuclei - Halo06

Workshop: The Physics of Halo Nuclei

30th October 2006 for 1 week, at ECT*, Trento, Italy

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Talks at the Workshop

Tom Aumann: Electromagnetic dissociation of halo nuclei (pdf)

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.

Daniel Baye: Dynamical eikonal approximation of breakup reactions (pdf)

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.

Angela Bonaccorso: Unbound exotic nuclei studied via projectile fragmentation (ppt)


Pierre Capel: What do we actually probe in breakup reactions? (pdf)

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.

Raquel Crespo: Elastic & inelastic scattering from halo nuclei (pdf)


Boris Danilin:  Correlations in the three body continuum (ppt)

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.

Barry Davids: Transfer reactions with halo nuclei (ppt)

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.

Pierre Descouvemont: Three-body continuum states (pdf)


Hans Feldmeier: Halo and Cluster Structures in Fermionic Molecular Dynamics (pdf)


António Fonseca: Three-body scattering with two-charged particles: application to direct nuclear reactions (pdf)


Christian Forssén:  Large-basis ab initio shell model investigations of halo nuclei (pdf)

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.

Mahir Hussein, Scaling and interference in breakup (pdf)

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

F. Miguel Marques: Probing correlations in many-neutron systems (pdf)


Takashi Nakamura, Invariant mass spectroscopy of halo nuclei at intermediate energies (pdf)

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)

Petr Navratil: Helium radii and proton analyzing powers in the NCSM (pdf)


Chiara Nociforo, 11Be and the evolution of the shell structure (pdf)

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.

Filomena Nunes: Recent developments in the study of halo breakup (ppt)

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.

Manuela Rodríguez-Gallardo: 6He scattering within THO-CDCC framework (pdf)

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.

Robert Roth: Ab Initio Nuclear Structure for Exotic Nuclei based on VUCOM (pdf)

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.

Haik Simon:  Correlation studies in breakup experiments (pdf)

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.

Jeff Tostevin, Knockout and breakup reactions (pdf)

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.

Jan Vaagen, Quo Vadis - Halo? (pdf)

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.                    Webmaster: