303 research outputs found
A Multi-Configuration Mixing Approach with Symmetry-Projected Complex Hartree-Fock-Bogoliubov Determinants
A multi-configuration mixing approach built on essentially complex,
symmetry-projected Hartree-Fock-Bogoliubov (HFB) mean fields is introduced. The
mean fields are obtained by variation after projection. The configuration space
consists out of the symmetry-projected HFB vacuum and the symmetry-projected
two-quasiparticle excitations for even, and the symmetry-projected
one-quasiparticle excitations for odd A systems. The underlying complex HFB
transformations are assumed to be time-reversal invariant and axially
symmetric. The model allows nuclear structure calculations in large model
spaces with arbitrary two-body interactions. The approach has been applied to
Ne and Ne. Good agreement with the exact shell model results and
considerable improvement with respect to older calculations, in which only real
HFB transformations were admitted, is obtained.Comment: 30 pages LaTeX file, 4 Postscript figure
Translationally invariant calculations of form factors, nucleon densities and momentum distributions for finite nuclei with short-range correlations included
Relying upon our previous treatment of the density matrices for nuclei (in
general, nonrelativistic self-bound finite systems) we are studying a combined
effect of center-of-mass motion and short-range nucleon-nucleon correlations on
the nucleon density and momentum distributions in light nuclei ( and
). Their intrinsic ground-state wave functions are constructed in the
so-called fixed center-of-mass approximation, starting with mean-field Slater
determinants modified by some correlator (e.g., after Jastrow or Villars). We
develop the formalism based upon the Cartesian or boson representation, in
which the coordinate and momentum operators are linear combinations of the
creation and annihilation operators for oscillatory quanta in the three
different space directions, and get the own "Tassie-Barker" factors for each
distribution and point out other model-independent results. After this
separation of the center-of-mass motion effects we propose additional analytic
means in order to simplify the subsequent calculations (e.g., within the
Jastrow approach or the unitary correlation operator method). The charge form
factors, densities and momentum distributions of and
evaluated by using the well known cluster expansions are compared with data,
our exact (numerical) results and microscopic calculations.Comment: 19 pages, 6 figure
Anomalous Crossing Frequency in Odd Proton Nuclei
A generic explanation for the recently observed anomalous crossing
frequencies in odd proton rare earth nuclei is given. As an example, the proton
band in Ta is discussed in detail by using the
angular momentum projection theory. It is shown that the quadrupole pairing
interaction is decisive in delaying the crossing point and the changes in
crossing frequency along the isotope chain are due to the different neutron
shell fillings
Dirac Hartree-Fock for Finite Nuclei Employing realistic Forces
We discuss two different approximation schemes for the self-consistent
solution of the {\it relativistic} Brueckner-Hartree-Fock equation for finite
nuclei. In the first scheme, the Dirac effects are deduced from corresponding
nuclear matter calculations, whereas in the second approach the local-density
approximation is used to account for the effects of correlations. The results
obtained by the two methods are very similar. Employing a realistic
one-boson-exchange potential (Bonn~A), the predictions for energies and radii
of O and Ca come out in substantially better agreement with
experiment as compared to non-relativistic approaches. As a by-product of our
study, it turns out that the Fock exchange-terms, ignored in a previous
investigation, are not negligible.Comment:
Projection and ground state correlations made simple
We develop and test efficient approximations to estimate ground state
correlations associated with low- and zero-energy modes. The scheme is an
extension of the generator-coordinate-method (GCM) within Gaussian overlap
approximation (GOA). We show that GOA fails in non-Cartesian topologies and
present a topologically correct generalization of GOA (topGOA). An RPA-like
correction is derived as the small amplitude limit of topGOA, called topRPA.
Using exactly solvable models, the topGOA and topRPA schemes are compared with
conventional approaches (GCM-GOA, RPA, Lipkin-Nogami projection) for
rotational-vibrational motion and for particle number projection. The results
shows that the new schemes perform very well in all regimes of coupling.Comment: RevTex, 12 pages, 7 eps figure
Ab-initio calculation of the binding energy with the Hybrid Multideterminant scheme
We perform an ab-initio calculation for the binding energy of using
the CD-Bonn 2000 NN potential renormalized with the Lee-Suzuki method. The
many-body approach to the problem is the Hybrid Multideterminant method. The
results indicate a binding energy of about , within a few hundreds KeV
uncertainty. The center of mass diagnostics are also discussed.Comment: 18 pages with 3 figures. More calculations added, to be published in
EPJ
Momentum and Energy Distributions of Nucleons in Finite Nuclei due to Short-Range Correlations
The influence of short-range correlations on the momentum and energy
distribution of nucleons in nuclei is evaluated assuming a realistic
meson-exchange potential for the nucleon-nucleon interaction. Using the
Green-function approach the calculations are performed directly for the finite
nucleus O avoiding the local density approximation and its reference to
studies of infinite nuclear matter. The nucleon-nucleon correlations induced by
the short-range and tensor components of the interaction yield an enhancement
of the momentum distribution at high momenta as compared to the Hartree-Fock
description. These high-momentum components should be observed mainly in
nucleon knockout reactions like leaving the final nucleus in a state
of high excitation energy. Our analysis also demonstrates that non-negligible
contributions to the momentum distribution should be found in partial waves
which are unoccupied in the simple shell-model. The treatment of correlations
beyond the Brueckner-Hartree-Fock approximation also yields an improvement for
the calculated ground-state properties.Comment: 12 pages RevTeX, 7 figures postscript files appende
Neuroendocrine Tumors of the Bronchopulmonary System (Typical and Atypical Carcinoid Tumors): Current Strategies in Diagnosis and Treatment. Conclusions of an Expert Meeting February 2011 in Weimar, Germany
Neuroendocrine tumors (NETs; syn. carcinoid tumors) are highly or moderately differentiated neoplasms. They comprise a large variety of rare and heterogeneous tumors with an estimated incidence of 3-5/100,000/year. They can arise in virtually every internal organ, but mainly occur in the gastroenteropancreatic and bronchopulmonary systems. Around 25% of the NETs are localized in the bronchopulmonary system. Approximately 2% of all lung tumors are NETs. According to the World Health Organization (WHO) classification of lung tumors, bronchopulmonary NETs are subdivided into typical carcinoids (TCs) and atypical carcinoids (ACs). The parameter with the highest impact on NET behavior and prognosis is the histological classification and staging according to the tumor/node/metastasis (TNM) system. The diagnosis of NETs is established by histological examination and the immunohistochemical detection of general neuroendocrine markers, such as chromogranin A (CgA) and synaptophysin. Serum markers and the use of functional imaging techniques are important additive tools to establish the diagnosis of a NET. The only curative option for lung NETs is complete surgical resection. Beyond that, the currently available interdisciplinary therapeutic options are local ablation, biotherapy (somatostatin analogues), or chemotherapy. New therapeutic options such as peptide receptor radionuclide therapy (PRRT) and molecularly targeted therapies achieve promising results and are under further evaluation. This report is a consensus summary of the interdisciplinary symposium âNeuroendocrine Tumors of the Lung and of the Gastroenteropancreatic System (GEP NET) - Expert Dialogue' held on February 25-26, 2011 in Weimar, Germany. At this conference, a panel of 23 German experts shared their knowledge and exchanged their thoughts about research, diagnosis, and clinical management of NETs, whereby special attention was paid to NETs of the respiratory trac
Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS
We present the results of a search for new, heavy particles that decay at a
significant distance from their production point into a final state containing
charged hadrons in association with a high-momentum muon. The search is
conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV
and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS
detector operating at the Large Hadron Collider. Production of such particles
is expected in various scenarios of physics beyond the standard model. We
observe no signal and place limits on the production cross-section of
supersymmetric particles in an R-parity-violating scenario as a function of the
neutralino lifetime. Limits are presented for different squark and neutralino
masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final
version to appear in Physics Letters
Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment
This paper describes an analysis of the angular distribution of W->enu and
W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with
the ATLAS detector at the LHC in 2010, corresponding to an integrated
luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and
the missing transverse energy, the W decay angular distribution projected onto
the transverse plane is obtained and analysed in terms of helicity fractions
f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV
and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw
> 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour,
are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017
+/- 0.030, where the first uncertainties are statistical, and the second
include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables,
revised author list, matches European Journal of Physics C versio
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