Interaction of optical lasers with atomic nuclei.
Nuclear transitions induced by an optical laser coupled to atomic electrons are examined in the context of a soluble model obtained by replacing the Coulomb field of the electrons by a harmonic oscillator. The results indicate that present lasers are marginal for causing this effect, but reasonable extrapolations in intensity and frequency would lead to experimental tests. Choosing the oscillator constant to reproduce realistic atomic radii results in nuclear electric dipole transitions that are potentially observable but that higher electric moments will be too small.

title: 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 ) .

title: 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.

title: Limits on the lifetime of the shape isomer of 238U.

title: Low-lying spectroscopy of a few even-even silicon isotopes investigated by means of the multiparticle-multihole Gogny energy density functional
abstract: 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.

title: FISSION COLLECTIVE DYNAMICS IN A MICROSCOPIC FRAMEWORK
abstract: 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.

title: Bottom-quark production at hadron colliders.
abstract: The recent measurement by the UA1 group of the cross section for bottom-quark production with transverse momentum greater than 5 GeV is found to be in good agreement with the simplest, lowest-order computations in perturbative quantum chromodynamics. This may be contrasted with the well-known disagreement for the much lighter charm quark. Further checks are discussed.

title: Isolated prompt photon production in hadronic final states of e+e- annihilation.
abstract: 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.

title: Transverse momentum distributions for heavy quark pairs.
abstract: We study the transverse momentum distribution for a [ital pair] of heavy quarks produced in hadron-hadron interactions. Predictions for the large transverse momentum region are based on exact order [alpha][sub [ital s]][sup 3] QCD perturbation theory. For the small transverse momentum region, we use techniques for all orders resummation of leading logarithmic contributions associated with initial state soft gluon radiation. The combination provides the transverse momentum distribution of heavy quark pairs for all transverse momenta. Explicit results are presented for [ital b[bar b]] pair production at the Fermilab Tevatron collider and for [ital c[bar c]] pair production at fixed target energies.

title: Measurement of the B semileptonic branching fraction with lepton tags.
abstract: We have used the CLEO II detector and 2.06fb^(-1) of ϒ(4S) data to measure the B-meson semileptonic branching fraction. The B→Xeν momentum spectrum was obtained over nearly the full momentum range by using charge and kinematic correlations in events with a high-momentum lepton tag and an additional electron. We find B(B→Xeν) = (10.49±0.17±0.43)%, with overall systematic uncertainties less than those of untagged single-lepton measurements. We use this result to calculate the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element V_(cb) and to set an upper limit on the fraction of ϒ(4S) decays to final states other than BB .

title: Calculations of prompt-photon production in QCD.
abstract: 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.