121195897
Symmetries of the nuclear average field hamiltonian and a search for possible exotic equilibrium deformations in superdeformed nuclei
Abstract Symmetry properties of the general average-field hamiltonian-matrix resulting from the geometrical symmetries of the hamiltonian itself are derived and discussed. The corresponding numerical algorithms are constructed. Total energy calculations for superdeformed nuclei are then extended to include the usually neglected deformation modes α λ = 3 μ ≠ 0 in the expansion of the nuclear surface expression R(ϑ, ϕ; {α}) = c ({α}) R 0 1+ ∑ λ ∑ μ=−λ λ α λμ ∗ Y λμ (ϑφ) . The general trends in the shell-energy dependence on α λ = 3 μ and the implied instabilities in the superdeformed configurations of the rare earth nuclei are studied using the Strutinsky formula with the macroscopic part taken in the form of the folded-Yukawa plus exponential interaction. A possibility of new (double superdeformed minimum) structures coexisting in some nuclei and resulting from the proton shell effects is predicted and illustrated. No signficant neutron effects are found in the rare superdeformed nuclei considered.
119356133
The Shears Mechanism in 142Gd in the Skyrme-Hartree-Fock Method with the Tilted-Axis Cranking
We report on the first Skyrme-Hartree-Fock calculations with the tilted-axis cranking in the context of magnetic rotation. The mean field symmetries, differences between phenomenological and self-consistent methods and the generation of shears-like structures in the mean field are discussed. Significant role of the time-odd spin-spin effective interaction is pointed out. We reproduce the shears mechanism, but quantitative agreement with experiment is rather poor. It may have to do with too large core polarization, lack of pairing correlations or properties of the Skyrme force.
23672287
Superdeformation in the quasicontinuum: Microscopic view of the excited superdeformed bands and the corresponding level densities.
Microscopic calculations of both the normal and the superdeformed rotational bands have been performed for a number of rare earth nuclei. The universal'' Woods-Saxon potential and the extended Strutinsky method have been used. Excited bands up to a prescribed energy limit {ital E}{sup *} (usually 2.5 to 3.5 MeV) have been calculated individually by minimizing the corresponding nuclear energies over the quadrupole and hexadecapole deformations. This turns out to be essential, when comparing with experimental results for the known discrete bands. An important influence of the superdeformed neutron ({ital N}=86) shell closure on the microscopically calculated rotational-level densities is illustrated and discussed.
119453196
Search for the Jacobi shape transition in light nuclei
Abstract.The $\gamma$-rays following the reaction 105 MeV 18O + 28Si have been measured using the EUROBALL IV, HECTOR and EUCLIDES arrays in order to investigate the predicted Jacobi shape transition. The high-energy $\gamma$-ray spectrum from the GDR decay indicates the presence of large deformations in the hot 46Ti nucleus, in agreement with new theoretical calculations based on the rotating liquid-drop model.
24677742
Critical frequency in nuclear chiral rotation.
Self-consistent solutions for the so-called planar and chiral rotational bands in 132La are obtained for the first time within the Skyrme-Hartree-Fock cranking approach. It is suggested that the chiral rotation cannot exist below a certain critical frequency which under the approximations used is estimated as Planck's omega(crit) approximately 0.5-0.6 MeV. However, the exact values of Planck's omega(crit) may vary, to an extent, depending on the microscopic model used, in particular, through the pairing correlations and/or calculated equilibrium deformations. The existence of the critical frequency is explained in terms of a simple classical model of two gyroscopes coupled to a triaxial rigid body.
16534405
Solution of the Skyrme—Hartree—Fock equations in the Cartesian deformed harmonic oscillator basis II. The program HFODD
Abstract We describe a method of solving the nuclear Skyrme-Hartree-Fock problem by using a deformed Cartesian harmonic oscillator basis. The complete list of expressions required to calculate local densities, total energy, and self-consistent fields is presented, and an implementation of the self-consistent symmetries is discussed. Formulas to calculate matrix elements in the Cartesian harmonic oscillator basis are derived for the nuclear and Coulomb interactions.
118476812
Energy dependence of the $\rho$ resonance in $\pi\pi$ elastic scattering from lattice QCD
We determine the energy-dependent amplitude for elastic {pi} {pi} P-wave scattering in isospin-1 by computing part of the discrete energy spectrum of QCD in finite cubic boxes. We observe a rapidly rising phase shift that can be well described by a single {rho} Resonance. The spectrum is obtained from hadron correlators computed using lattice QCD with light quark masses corresponding to m{sub {pi}}~400 MeV. Variational analyses are performed with large bases of hadron interpolating fields including, as well as fermion bilinears that resemble q{anti q} Constructions, also operators that look like pairs of pions with definite relative and total momentum. We compute the spectrum for a range of center-of-mass momenta and in various irreducible representations of the relevant symmetry group. Hence we determine more than thirty values of the isospin-1 P-wave scattering phase shift in the elastic region, mapping out its energy dependence in unprecedented detail.
11255729
Two-photon decays of charmonia from lattice QCD.
We make the first calculation in lattice QCD of two-photon decays of mesons. Working in the charmonium sector, using the Lehmann-Symanzik-Zimmermann reduction to relate a photon to a sum of hadronic vector eigenstates, we compute form factors in both the spacelike and timelike domains for the transitions eta c --> gamma*gamma* and chi(c0) --> gamma*gamma*. At the on-shell point, we find approximate agreement with experimental world-average values.
119358065
Options for the SELEX state D+(sJ)(2632)
Abstract We consider possible assignments for the D s J + ( 2632 ) , which was recently reported in D s + η and D 0 K + final states by the SELEX Collaboration at Fermilab. The most plausible quark model assignment for this state is the first radial excitation ( 2 3 S 1 ) of the c s ¯ D s * ( 2112 ) , although the predicted mass and strong decay branching fractions for this assignment are not in agreement with the SELEX data. The reported dominance of D s η over DK appears especially problematic. An intriguing similarity to the K * ( 1414 ) is noted. 2 3 S 1 – D 1 3 configuration mixing is also considered, and we find that this effect is unlikely to resolve the branching fraction discrepancy. Other interpretations as a c s ¯ -hybrid or a two-meson molecule are also considered, but appear unlikely. Thus, if this state is confirmed, it will require reconsideration of the systematics of charmed meson spectroscopy and strong decays.
121740666
Baryon spectroscopy in lattice QCD with spin identification
Lattice QCD calculations are presented for the spectra of N* excited states with spins up to J = 7/2. The lattice operators and analysis methods used to identify the continuum spins in the lattice calculations are reviewed. In simulations with mπ ≥ 392 MeV, the low-lying excited states of lattice QCD are found to have the same quantum numbers as the states of SU(6) ⊗O(3) symmetry. The lattice spectra are inconsistent with either a quark-diquark model or parity doubling of states.
121414612
Gluonic excitations in the hadronic spectrum
QCD at low energy features a gluonic field that is strongly coupled to itself and to quarks. I will present a summary of what we know about the role that excitations of the gluonic field play in determining the spectrum of meson resonances. Recent studies using lattice techniques have suggested a phenomenology of gluonic excitations within QCD that leads to hybrid mesons with both exotic and non-exotic quantum numbers. I will discuss these calculations and describe their relationship to current experimental knowledge and to forthcoming experiments at Jefferson Lab and elsewhere.