16434102
Pentaquark symmetries, selection rules and another potentially narrow state
Abstract We identify essential differences between the pentaquark and chiral soliton models of 10 5 and 8 5 pentaquarks and conventional 8 3 states, which are experimentally measurable. We show how the decays of Ξ5 states in particular can test models of the pentaquarks, recommend study of the relative branching ratios of, e.g., Ξ − 5 →Ξ − π 0 :Ξ 0 π − , and predict that the decay amplitude Ξ 5 →Ξ ∗ π is zero at leading order in pentaquark models for any mixture of 10 and the associated 8 5 . We also include a pedagogic discussion of wavefunctions in the pentaquark picture and show that pentaquark models have this 8 5 with F/D=1/3, in leading order forbidding Ξ5→ΛK. The role of Fermi–Dirac symmetry in the qqqq wavefunction and its implications for the width of pentaquarks are briefly discussed. The relative couplings g 2 (Θ Q NK Q ∗ )/g 2 (Θ Q NK Q )=3 for Q≡s,c,b. A further potentially narrow state Λ in 8 5 with JP=3/2+ is predicted around 1650 MeV.
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.
14262604
Hybrid meson production by electromagnetic and weak interactions in a flux tube simulation of lattice QCD
We calculate rates for hybrid meson production by electromagnetic and weak interactions in the flux-tube model. Applications include photo and electroproduction at Jefferson Laboratory and HERA, and the production of light strange and charmed hybrids in the weak decays of heavy flavours. Photoproduction of some light hybrids is predicted to be prominent in charge exchange reactions, $\gamma p \to n \cal{H}$ and accessible in $\gamma p \to p \cal{H}$. Production of light or charmed hybrids in $B$ and $D$ decays may be feasible with high statistics. Photoproduction of the axial hybrid meson is predicted to be large courtesy of $\pi$ exchange, and its strange counterpart is predicted in $B \to \psi K_H(1^+)$ with $b.r. \sim 10^{-4}$. Production rates for exotic hybrid candidates $1^{-+};(0,2)^{+-}$ are given special attention. Selection rules that can help to distinguish between hybrid and conventional states with the same $J^{PC}$ are noted.
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.
16902153
TOWARDS EXPLANATION OF THE "INERTIA ANOMALIES" IN REALISTIC MEAN FIELD CALCULATIONS
Careful theoretical studies of the nuclear collective inertia based on the non-relativistic mean-field theory and the cranking model indicate that the moments of inertia of the super-deformed nuclei calculated using various standard methods and parameterizations exceed systematically the experimental values. Similarly, but for other reasons the relativistic cranking calculations based on the relativistic mean field method present, in our opinion, a different class of systematic deviations from experiment. The origin and possible explanations of these deviations are discussed briefly.
119475372
QUANTUM ROTATIONAL SPECTRA AND CLASSICAL ROTORS
We consider the generalized rotor Hamiltonians capable of describing quantum systems invariant with respect to symmetry point-groups that go beyond the usual D2-symmetry of a tri-axial rotor. We discuss the canonical de-quantisation procedure to obtain the classical analogs of the original quantum Hamiltonians. Classical and quantum solutions to the Hamiltonians relevant in the nuclear physics applications are illustrated and compared using the 'usual' (D2) and an 'exotic' (Td) symmetries.
55630915
Probing nuclear shapes close to the fission limit with the giant dipole resonance in 216 Rn
The gamma-ray decay of the giant dipole resonance (GDR) in the compound nucleus {sup 216}Rn formed with the reaction {sup 18}O+{sup 198}Pt at the bombarding energy of 96 MeV was investigated. High-energy gamma-ray spectra in coincidence with both prompt and delayed low-energy transitions were measured. The obtained GDR width at the average temperature {approx_equal}1 MeV was found to be larger than that at T=0 MeV and to be approximately constant as a function of spin. The measured width value of 7 MeV is found to be consistent with the predictions based on calculations of the nuclear shape distribution using the newest approach for the treatment of the fission barrier within the liquid drop model. The present study is the first investigation of the giant dipole resonance width from the fusion-evaporation decay channel in this nuclear mass range.
122414594
Nuclear shell structure at very high angular momentum
Abstract A cranked modified-oscillator model (with triaxial shape coordinates ϵ and γ) is used to study the nuclear potential-energy surface (based on a Strutinsky type of shell correction method) for very high angular momenta (30 ≦ I ≦ 100). For this region of spin, pair correlation is assumed to have collapsed. The influence of rapid rotation on the shell structure has been studied in the light and heavy rare-earth region as well as the Te-Ba region. Preliminary studies have also been made in the regions of superheavy and light nuclei. The possible occurrence of yrast traps is discussed.