206321492
Hartree-Fock-Bogoliubov predictions for shape isomerism in nonfissile even-even nuclei.
Secondary minima in the potential-energy surfaces of even-even nuclei are searched for through nonaxial Hartree-Fock-Bogoliubov calculations based on a finite-range, density-dependent effective force. This study covering the mass region 64/lt//ital A//lt/208 is intended to select nonfissile nuclei which would develop shape isomers. Results are presented for nuclei which seem to be the most interesting candidates for experimental investigations.
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 ) .
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.
38420080
Limits on the lifetime of the shape isomer of 238U.
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.
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.
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.
45469707
Prompt photon production with a polarized deuteron target.
Predictions are presented of the polarization asymmetry in prompt photon production at large transverse momentum in the scattering of longitudinally polarized protons from longitudinally polarized deuteron targets. Data would provide important constraints on the polarization asymmetry of the gluon density in a nucleon. The experiments could take advantage of recent advances in the technology of polarized {sup 6}LiD.
706059
Calculations of prompt-photon production in QCD.
Cross sections for prompt-photon production at collider energies are not strictly inclusive because an isolation requirement is imposed whereby the photon is detected only if accompanied by a restricted amount of hadronic energy. In this paper we provide a consistent treatment of the isolated prompt-photon cross section in QCD perturbation theory. The isolation requirement reduces sensitivity of the cross section to poorly known long-distance fragmentation contributions. However, the normal cancellation of infrared singularities is upset by the isolation cutoffs, rendering the short-distance perturbative calculation highly nontrivial. In our solution we address both the short- and the long-distance issues in detail, showing that well-behaved predictions can be derived for a wide range of isolation parameters. Calculated cross sections are presented at several energies and scale dependence of the cross section is examined.
32381552
Nuclear effects in deep-inelastic lepton scattering.
We present a detailed study of a conventional nuclear model in which the observed differences between the deep-inelastic structure functions of nuclei and of free nucleons, F/sub 2/(x,Q/sup 2/) and q-bar(x,Q/sup 2/), are due to scattering from exchange pions in nuclei associated with the mechanisms responsible for nuclear binding. We assume that the quark and antiquark momentum distributions of these nucleons and pions are unaffected by the nuclear medium. We write the nuclear structure functions as a sum of convolutions of (measured) isolated-hadron structure functions with hadron momentum distributions derived from nuclear potential models. We show that all but one feature of deep-inelastic neutrino and charged-lepton data are reproduced by our model. The exception is the magnitude of the excess above unity of the ratio F/sub 2//sup A/(x)/F/sub 2//sup D/(x) for x<0.2, observed only by the European Muon Collaboration (EMC) experiment. If these EMC data are reduced in normalization by 5%, consistent with experimental uncertainties, then all features of the data are reproduced. We stress the importance of new neutrino and muon measurements at small x.
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