6451793
Mean-field description of ground-state properties of drip-line nuclei: Pairing and continuum effects.
Ground-state properties of exotic even-even nuclei with extreme neutron-to-proton ratios are described in the framework of self-consistent mean-field theory with pairing formulated in coordinate space. This theory properly accounts for the influence of the particle continuum, which is particularly important for weakly bound systems. The pairing properties of nuclei far from stability are studied with several interactions emphasizing different aspects, such as the range and density dependence of the effective interaction. Measurable consequences of spatially extended pairing fields are presented, and the sensitivity of the theoretical predictions to model details is discussed. {copyright} {ital 1996 The American Physical Society.}
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.
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.
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.
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.
6560227
Isolated prompt photon production in hadronic final states of e+e- annihilation.
We provide complete analytic expressions for the isolated prompt photon production cross section in e+e− annihilation reactions through one-loop order in quantum chromodynamics (QCD) perturbation theory. Functional dependences on the isolation cone size δ and isolation energy parameter ǫ are derived. The energy dependence as well as the full angular dependence of the cross section on θγ are displayed, where θγ specifies the direction of the photon with respect to the e+e− collision axis. We point out that conventional perturbative QCD factorization breaks down for isolated photon production in e+e− annihilation reactions in a specific region of phase space. We discuss the implications of this breakdown for the extraction of fragmentation functions from e+e− annihilation data and for computations of prompt photon production in hadron-hadron reactions.
21234668
Comparison of bottom-quark production rates in ISAGET with a full QCD 2-->3 calculation.
High-statistics samples of events have been generated with the ISAGET Monte Carlo simulation program in a study of bottom-quark production in proton-antiproton collisions at {radical}{ital s} =630 and 1800 GeV. These samples include lowest-order QCD production, flavor excitation, and gluon splitting contributions. Both Eichten-Hinchliffe-Lane-Quigg and Diemoz-Ferroni-Longo-Martinelli structure functions have been used. The integral transverse-momentum distribution {sigma}{sub {ital T}}({ital p}{sub {ital T},}{ital b}{gt}{ital p}{sub {ital T},min}) is presented for each data set. Results are compared to a full analytical next-to-leading-order calculation of Nason, Dawson, and Ellis. We find that ISAGET cross sections at large {ital p}{sub {ital T}} are greater than the results obtained in the analytical calculation. In addition, the ratio of the full cross section to the lowest-order result ({ital K} factor) can be as large as a factor of 2 greater than the analytical result, depending on {radical}{ital s} and {ital p}{sub {ital T}}. We discuss the implications of these overestimates that relate to the phenomenology of heavy-flavor production, notably searches for the top quark.
10820318
Implications of bottom-quark cross section data at hadron collider energies.
In next-to-leading-order {ital O}({alpha}{sub {ital s}}{sup 3}) quantum chromodynamics, gluon-gluon interactions are the dominant mechanism for the production of bottom quarks at CERN and Fermilab hadron collider energies at values of momentum transfer currently accessible. There is a notable discrepancy between the data from the Collider Detector at Fermilab and existing {ital O}({alpha}{sub {ital s}}{sup 3}) theoretical calculations. Using these data, in conjunction with data from deep-inelastic lepton scattering, we show that it is possible to determine a new gluon density whose shape differs substantially from that derived from previous fits to data. Other implications of the data are discussed.
14220763
Production of a prompt photon in association with a charm quark at next-to-leading order in QCD.
A second order $O({\ensuremath{\alpha}}_{s}^{2})$ calculation in perturbative quantum chromodynamics of the two particle inclusive cross section is presented for the reaction $p+\overline{p}\ensuremath{\rightarrow}\ensuremath{\gamma}+c+X$ for large values of the transverse momentum of the prompt photon and charm quark. The combination of analytic and Monte Carlo integration methods used here to perform phase-space integrations facilitates the imposition of photon isolation restrictions and other selections of relevance in experiments. Differential distributions are provided for various observables. Positive correlations in rapidity are predicted.