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.
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.
43587069
High spin states in 75Kr: Approaching superdeformation in the A=80 region.
Excited states in {sup 75}Kr were populated via the reaction {sup 46}Ti({sup 32}S,2{ital pn}) at a beam energy of 97 MeV. Several new high-spin states were found. Evidence for band crossings was found in both the positive- and negative-parity bands. Calculations using a cranked Strutinsky-Bogolyubov model with a Woods-Saxon potential indicate noticeably different deformations for the opposite parity bands: {beta}{sub 2}=0.40, {gamma}={minus}8{degree} for the positive-parity band and {beta}{sub 2}=0.36, {gamma}=3{degree} for the negative-parity band. These deformations are comparable to superdeformations reported by other authors in the cerium region. Signature splitting in both positive- and negative-parity bands was well reproduced by the calculations. Indirect evidence suggests shape coexistence within the positive-parity band at low spin.
593218
Deformed atomic nuclei with degeneracies of the nucleonic levels higher than 2.
As it is well known, the single-nucleonic levels in a nucleus manifest either the Kramers degeneracy {ital d}=2, or, if a nucleus is spherical, a trivial ``magnetic`` degeneracy {ital d}=2{ital j}+1. It will be shown using the results of the realistic total nuclear energy calculations that a possibility of a fourfold degenerate levels exists in a number of {ital N}{similar_to}136 isotones due to their high intrinsic symmetry. Those exotic states are predicted to be isometric; they lie only a few hundreds of keV above the ground state. Other possible nuclear regions where the same mechanism may take place are indicated.
119034107
Evidence for the Jacobi shape transition in hot 46Ti
The gamma-rays from the decay of the GDR in 46Ti compound nucleus formed in the 18O+28Si reaction at bombarding energy 105 MeV have been measured in an experiment using a setup consisting of the combined EUROBALL IV, HECTOR and EUCLIDES arrays. A comparison of the extracted GDR lineshape data with the predictions of the thermal shape fluctuation model shows evidence for the Jacobi shape transition in hot 46Ti. In addition to the previously found broad structure in the GDR lineshape region at 18-27 MeV caused by large deformations, the presence of a low energy component (around 10 MeV), due to the Coriolis splitting in prolate well deformed shape, has been identified for the first time.
39231887
Pairing, temperature, and deformed-shell effects on the properties of superdeformed 152Dy nucleus.
The existence of superdeformed shell closures together with pairing and the nuclear temperature effects are shown to explain the originally unexpected properties of the superdeformed band observed up to Iapprox.60(h/2..pi..) in the /sup 152/Dy nucleus. No parameters were adjusted to the superdeformed band properties. Population, and depopulation of the superdeformed bands, the moments of inertia, and side feeding properties are discussed and qualitatively understood. The use of the free-energy calculation results and the microcanonical ensemble formulation of the level-density problem at high-spin are proposed and discussed.
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.
54655904
Excited state baryon spectroscopy from lattice QCD
Here, we present a calculation of the Nucleon and Delta excited state spectrum on dynamical anisotropic clover lattices. A method for operator construction is introduced that allows for the reliable identification of the continuum spins of baryon states, overcoming the reduced symmetry of the cubic lattice. Using this method, we are able to determine a spectrum of single-particle states for spins up to and including J = 7/2, of both parities, the first time this has been achieved in a lattice calculation. We find a spectrum of states identifiable as admixtures of SU(6) Ⓧ O(3) representations and a counting of levels that is consistent with the non-relativistic $qqq$ constituent quark model. This dense spectrum is incompatible with quark-diquark model solutions to the "missing resonance problem" and shows no signs of parity doubling of states.
125997156
Charmonium Radiative Physics
123280722
CHARMONIUM EXCITED STATES FROM LATTICE QCD
We apply the variational method with a large basis of interpolating operators to demonstrate the feasibility of extracting multiple excited states in charmonium from lattice QCD. The calculation is performed in the quenched approximation to QCD, using the clover fermion action on an anisotropic lattice. A crucial element of our approach is a knowledge of the continuum limit of the interpolating operators, providing important additional information on the spin assignment of the states, even at a single value of the lattice spacing. Though we find excited-state masses that are systematically high with respect to the quark potential model, and the experimental masses where known, we attribute this as most likely an artifact of the quenched approximation.
119183361
Charmonium in lattice QCD and the nonrelativistic quark model
We compare the results of a numerical lattice QCD calculation of the charmonium spectrum with the structure of a general nonrelativistic potential model. To achieve this we form the nonrelativistic reduction of derivative-based fermion bilinear interpolating fields used in lattice QCD calculations and compute their overlap with cc meson states at rest constructed in the nonrelativistic quark model, providing a bound-state model interpretation for the lattice data. Essential gluonic components in the bound states, usually called hybrids, are identified by considering interpolating fields that involve the gluonic field-strength tensor and which have zero overlap onto simple cc model states.