41606550
Preliminary selection of candidates for shape isomerism from even-even nuclei with masses A<208.
This theoretical work represents the first stage in our efforts to establish an extensive list of nonfissile even-even nuclei located inside or near the valley of stability which might develop shape isomers. Our selection relies upon whether a secondary minimum takes place along an elongation axis in the potential energy surfaces of nuclei spread over the mass region A<208. These surfaces are determined through a joint use of the Hartree-Fock-Bogoliubov and Strutinsky methods. More than seventy nuclei located inside the region 40
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.
38420080
Limits on the lifetime of the shape isomer of 238U.
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 ) .
8335948
Momentum correlations in heavy-quark hadroproduction.
Predictions are presented of correlations in rapidity and in scaled longitudinal momentum (Feynman x/sub F/) for associated production of a bottom quark b and its antiquark in high-energy fixed-target and collider experiments. Rapidity correlations are positive but remarkably broad in the central region at current collider energies, extending a factor of 2 beyond the approx.2 units typical of short-range order.
21145414
Search for exclusive charmless hadronic B decays.
We have searched for two-body charmless hadronic decays of B mesons. Final states include ππ, Kπ, and KK with both charged and neutral kaons and pions: πρ, Kρ, and K^*π; and Kφ, K^*φ, and φφ. The data used in this analysis consist of 2.6×10^6 BB¯ pairs produced at the Υ(4S) taken with the CLEO II detector at the Cornell Electron Storage Ring (CESR). We measure the branching fraction of the sum of B^0→π^+π^- and B^0→K^+π^- to be (1.8_(-0.5-0.3)^(+0.6+0.2)±0.2)×10^(-5). In addition, we place upper limts on individual branching fractions in the range from 10^(-4) to 10^(-6).
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.
41410937
Prospects for supersymmetry at the Fermilab collider.
We compute cross sections for production of pairs of strongly interacting supersymmetric (SUSY) particles in p-italicp-bar collisions as a function of collider energy. For a scalar-quark or gluino mass of 80 GeV, we find that the ratio of the SUSY cross section to the standard-model background increases by a factor of about 10 when ..sqrt..s-italic is increased from 630 to 1600 GeV. If decays to photinos are dominant, we show that in the first 2 years of running, experiments at the Fermilab Tevatron collider should be sensitive to gluino (scalar-quark) masses up to at least m-italic/sub g-italic-tilde/ = 150 GeV (m-italic/sub q-italic-tilde/ = 120 GeV). We show characteristic missing-p-italic/sub T-italic/ distributions expected if SUSY particles with such masses are produced. For SUSY particles of large mass, we stress the importance of scalar-quark and gluino decays to W-italic and Z-italic gauginos.
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