38420080
Limits on the lifetime of the shape isomer of 238U.
121250172
Microscopic analysis of collective dynamics in low energy fission
Abstract A microscopic description based on the density-dependent Hartree-Fock-Bogolyubov approach with several kinds of constraints is used to extract the characteristic features of the collective dynamics of the fission process at low energy. The dynamical behaviour of the nucleus beyond the second saddle point and a mechanism for scission are deduced. They are analyzed in the framework of a quantum-mechanical treatment of collective dynamics taking into account the variations of the collective inertia.
122686083
FISSION COLLECTIVE DYNAMICS IN A MICROSCOPIC FRAMEWORK
A time-dependent microscopic approach of the fission process based on the constrained HFB approach with the Gogny force and the Hill and Wheeler configuration mixing method is described. Recent results concerning fragment distributions (mass, kinetic and deformation energies) and other fragment observables in 238U obtained with such an approach are presented and discussed.
16750672
The neutron halo in heavy nuclei calculated with the Gogny force
The proton and neutron density distributions, one- and two-neutron separation energies and radii of nuclei for which neutron halos are experimentally observed, are calculated using the self-consistent Hartree-Fock-Bogoliubov method with the effective interaction of Gogny. Halo factors are evaluated assuming hydrogen-like antiproton wave functions. The factors agree well with experimental data. They are close to those obtained with Skyrme forces and with the relativistic mean-field approach.
118436812
Low-lying spectroscopy of a few even-even silicon isotopes investigated by means of the multiparticle-multihole Gogny energy density functional
A multiconfiguration microscopic method has been applied with the Gogny effective interaction to the calculation of low-lying positive-parity states in even-even Si isotopes. The aim of the study is to compare the results of this approach with those of a standard method of GCM type and to get insight into the predictive power of multiconfiguration methods employed with effective nucleonnucleon force taylored to mean-field calculations. It is found that the multiconfiguration approach leads to an excellent description of the low-lying spectroscopy of Si, Si and Si, but gives a systematic energy shift in Si. A careful analysis of this phenomenon shows that this discrepancy originates from too large proton-neutron matrix elements supplied by the Gogny interaction at the level of the approximate resolution of the multiparticle-multihole configuration mixing method done in the present study. These proton-neutron matrix elements enter in the definition of both singleparticle orbital energies and coupling matrix elements. Finally, a statistical analysis of highly excited configurations in Si is performed, revealing exponential convergence in agreement with previous work in the context of the shell model approach. This latter result provides strong arguments towards an implicit treatment of highly excited configurations.
119216511
Microscopic transport theory of nuclear processes
Abstract We formulate a microscopic theory of the decay of a compound nucleus through fission which generalizes earlier microscopic approaches of fission dynamics performed in the framework of the adiabatic hypothesis. It is based on the constrained Hartree–Fock–Bogoliubov procedure and the Generator Coordinate Method, and requires an effective nucleon–nucleon interaction as the only input quantity. The basic assumption is that the slow evolution of the nuclear shape must be treated explicitly, whereas the rapidly time-dependent intrinsic excitations can be treated by statistical approximations. More precisely, we introduce a “reference density” ρ P which represents the slow evolution of the nuclear shape by a reduced density matrix and the state of intrinsic excitations by a canonical distribution at each given shape of the nucleus. The shape of the nuclear density distribution is described by parameters (“generator coordinates” q ), not by “superabundant” degrees of freedom introduced in addition to the complete set of nucleonic degrees of freedom. We first derive a rigorous equation of motion for the reference density ρ P and, subsequently, simplify this equation on the basis of the “Markov approximation”. The temperature T which appears in the canonical distribution is determined by the requirement that, at each time t , the reference density should correctly reproduce the mean excitation energy at given values of the shape parameters q . The resulting equation for the “local” temperature T ( q , t ) must be solved together with the equations of motion obtained for the reduced density matrix R ( q 1 , q 2 ; t ) .
6525412
Probing the weak-boson sector in Z gamma production at hadron colliders.
A detailed analysis of Zγ production at hadron colliders is presented for general ZZγ and Zγγ couplings. Deviations from the standard model gauge theory structure can be parametrized in terms of four ZZγ and four Zγγ form factors. The high-energy behavior of these form factors is severely restricted by unitarity. Prospects for testing the self-interactions of Z bosons and photons at the Fermilab Tevatron, the CERN Large Hadron Collider and the Superconducting Super Collider are explored. Sensitivity limits for anomalous ZZγ and Zγγ couplings are derived and compared to bounds from low-energy data and e + e − collider experiments
7775319
Perturbative resummed series for top quark production in hadron reactions.
Our calculation of the total cross section for inclusive production of {ital t{bar t}} pairs in hadron collisions is presented. The principal ingredient of the calculation is resummation of the universal leading-logarithm effects of gluon radiation to all orders in the quantum chromodynamics coupling strength, restricted to the region of phase space that is demonstrably perturbative. We derive the perturbative regime of the resummed series, starting from the principal-value resummation approach, and we isolate the perturbative domain in both moment space and, upon inversion of the corresponding Mellin transform, in momentum space. We show that our perturbative result does not depend on the manner nonperturbative or infrared effects are handled in principal-value resummation. We treat both the quark-antiquark and gluon-gluon production channels consistently in the MS factorization scheme. We compare our method and results with other resummation methods that rely on the choice of infrared cutoffs. We derive the renormalization or factorization scale dependence of our re- summed cross section, and we discuss factorization scheme dependence and remaining theoretical uncertainties, including estimates of possible nonperturbative contributions. We include the full content of the exact next-to-leading order calculation in obtaining our final results. We present predictions of the physical cross sectionmore » as a function of top quark mass in proton-antiproton reactions at center-of-mass energies of 1.8 and 2.0 TeV. We also provide the differential cross section as a function of the parton-parton subenergy. {copyright} {ital 1996 The American Physical Society.}« less
32525273
Search for CP violation in D0 decay.
R. Balest, K. Cho, W.T. Ford, M. Lohner, H. Park, P. Rankin, and J.G. Smith University of Colorado, Boulder, Colorado 80809 0890J.P. Alexander, C. Bebek, B.E. Berger, K. Berkelman, K. Bloom, T.E. Browder, * D.G. Cassel, H.A. Cho, D.M. Coffman, D.S. Crowcroft, M. Dickson, P.S. Drell, D.J. Dumas, R. Ehrlich, R. Elia, P. Gaidarev, M. Garcia-Sciveres, B. Gittelman, S.W. Gray, D.L. Hartill, B.K. Heltsley, S. Henderson, C.D. Jones, S.L. Jones, J. Kandaswamy, N. Katayama, P.C. Kim, D.L. Kreinick, T. Lee, Y. Liu, G.S. Ludwig, J. Masui, J. Mevissen, N.B. Mistry, C.R. Ng, E. Nordberg, J.R. Patterson, D. Peterson, D. Riley, and A. So8'er Cornell University, Ithaca, New York 1/858
22437567
Limits on flavor changing neutral currents in D0 meson decays.
Using the CLEO II detector at the Cornell Electron Storage Ring, we have searched for flavor changing neutral currents and lepton family number violations in D^0 meson decays. The upper limits on the branching fractions for D^0→l^+l^- and D^0→X^0l^+l^- are in the range 10^(-5) to 10^(-4), where X^0 can be a π^0, K_s^0, η, ρ^0, ω, K^(*0), or φ meson, and the l^+l^- pair can be e^+e^-, μ^+μ^-, or e^±μ^∓. Although these limits are above the theoretical predictions, most are new or an order of magnitude lower than previous limits.
27651738
Classification and JPG selection rules for weak currents.
Four categories are defined of exotic and nonexotic first-class and second-class weak currents, three of which are suppressed in the standard model. Hadronic final states produced through various symmetry-breaking mechanisms are subject to selection rules which govern their allowed values of J/sup P//sup G/. We show that there are four types of suppressed transitions and give examples of each.