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A microscopic theory for the decay of a compound nucleus is presented which is formulated in the spirit of transport theories. Its basic physical assumption is the existence of two time scales, a rapid one concerning the creation of intrinsic excitations and a slow one controlling the change of the nuclear shape. This fact is used in the derivation of an equation of motion for the reduced density by applying the so-called Markov approximation. A canonical distribution of the system with regard to the intrinsic excitations at a given shape is assumed as an approximation and a temperature T(q, t) depending on the nuclear shapes and time t is defined so as to render the canonical distribution as realistic as possible. [ABSTRACT FROM AUTHOR]

Two-dimensional Hartree-Fock-Bogoliubov (HFB) calculations have been performed from spherical shapes to large deformations with constraints on axial quadrupole and octupole deformations in 238U, 256–260Fm and 226Th actinides. Scission configurations have then been identified in this subspace of collective coordinates and many nuclear properties of the nascent fragments have been derived, such as deformation, deformation energy or prompt neutron multiplicity. The HFB states have then served as basis states for time-dependent collective calculations based on the Time-Dependent Generator Coordinate Method and the Gaussian Overlap Approximation to derive fission fragment yields. [ABSTRACT FROM AUTHOR]

A dynamical approach to the neutron-induced fission of 255,257Fm isotopes based on the time-dependent generator-coordinate method is applied. As the generating functions the eigensolutions of the constrained Hartree-Fock-Bogoliubov method with the effective D1S Gogny force are used. The here presented collective-dynamics calculations in the two-dimensional collective space described by quadrupole and octupole moments allow to determine the fragment mass distributions of those two Fm isotopes. [ABSTRACT FROM AUTHOR]

This continuation of the derivation of general beam-referenced stage-two spin-correlation functions is for the analysis of top–antitop pair-production at the Tevatron and at the Large Hadron Collider. Both the gluon-production and the quark-production contributions are included for the charged-lepton-plus-jets reaction pp or $p\bar{p}\rightarrow t\bar{t}\rightarrow(W^+b)(W^-\bar{b})\rightarrow(l^+\nu b)(W^-\bar{b})$ . There is a simple 4-angle beam-referenced spin-correlation function for determination of the relative sign of or for measurement of a possible non-trivial phase between the two dominant $\lambda_b=-1/2$ helicity amplitudes for the $t\rightarrow W^+b$ decay mode. There is an analogous function and tests for $\bar{t}\rightarrow W^-\bar{b}$ decay. This signature requires use of the $(t\bar{t})_{\text{c.m.}}$ energy of the hadronically decaying W-boson, or the kinematically equivalent cosine of the polar angle of $W^\mp$ emission in the antitop (top) decay frame. Spinors and their outer-products are constructed so that the helicity-amplitude phase convention of Jacob and Wick can be used throughout for the fixing of the signs associated with this large W-boson longitudinal–transverse interference effect. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Applying a variational multiparticle-multihole mixing method whose purpose is to include correlations beyond mean field in an unified way without particle number and Pauli violations, we investigate ground state properties of 22O nucleus, in the case of pairing-type correlations. The same interaction is used for the mean field and the residual part of the hamiltonian, namely, the density-dependent D1S Gogny force. [ABSTRACT FROM AUTHOR]

Most of this paper consists of the derivation of general beam-referenced stage-two spin-correlation functions for the analysis of top-antitop pair production at the Tevatron, at the Large Hadron Collider, and/or at an International Linear Collider. However, for the charged-lepton plus jets reaction $q \bar{q} \rightarrow t \bar{t} \rightarrow (W^ + b) (W^- \bar{b} ) \rightarrow (l^{ + } \nu b ) (W^- \bar{b} )$ , there is a simple three-angle spin-correlation function for the determination of the relative sign of or for the measurement of a possible non-trivial phase between the two dominant λ b=-1/2 helicity amplitudes for the t → W + b decay mode. For the CP-conjugate case, there is an analogous function and tests for $\bar{t} \rightarrow W^{-} \bar{b}$ decay. These results make use of W-boson longitudinal-transverse interference. [ABSTRACT FROM AUTHOR]

Theoretical results for giant resonances in the three doubly magic exotic nuclei 78Ni, 100Sn and 132Sn are obtained from Hartree-Fock (HF) plus Random Phase Approximation (RPA) calculations using the D1S parameterization of the Gogny two-body effective interaction. Special attention is paid to full consistency between the HF field and the RPA particle-hole residual interaction. The results for the exotic nuclei, on average, appear similar to those of stable ones, especially for quadrupole and octupole states. More exotic systems have to be studied in order to confirm such a trend. The low energy of the monopole resonance in 78Ni suggests that the compression modulus in this neutron-rich nucleus is lower than the one of stable ones. [ABSTRACT FROM AUTHOR]

A multiconfiguration microscopic method has been applied with the Gogny effective interaction to the calculation of low-lying positive-parity states in even-even 26,32Si isotopes. The aim of the study is to compare the results of this approach with those of a standard method of generator coordinate method (GCM) type and to get insight into the predictive power of multiconfiguration methods employed with effective nucleon-nucleon force tailored to mean-field calculations. It is found that the multiconfiguration approach leads to an excellent description of the low-lying spectroscopy of 26Si, 28Si, and 32Si, but gives a systematic energy shift in 30Si. 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 single-particle orbital energies and coupling matrix elements. Finally, a statistical analysis of highly excited configurations in 28Si is performed, revealing exponential convergence in agreement with previous work in the context of the shell model approach. This latter result provides strong arguments toward an implicit treatment of highly excited configurations. [ABSTRACT FROM AUTHOR]

Abstract: We present the first measurements of charge-dependent correlations on angular difference variables (pseudorapidity) and (azimuth) for primary charged hadrons with transverse momentum and from Au–Au collisions at . We observe correlation structures not predicted by theory but consistent with evolution of hadron emission geometry with increasing centrality from one-dimensional fragmentation of color strings along the beam direction to an at least two-dimensional hadronization geometry along the beam and azimuth directions of a hadron-opaque bulk medium. [Copyright &y& Elsevier]

Abstract: Identified mid-rapidity particle spectra of , , and from 200 GeV and collisions are reported. A time-of-flight detector based on multi-gap resistive plate chamber technology is used for particle identification. The particle-species dependence of the Cronin effect is observed to be significantly smaller than that at lower energies. The ratio of the nuclear modification factor () between protons () and charged hadrons (h) in the transverse momentum range is measured to be in minimum-bias collisions and shows little centrality dependence. The yield ratio of in minimum-bias collisions is found to be a factor of 2 lower than that in collisions, indicating that the Cronin effect alone is not enough to account for the relative baryon enhancement observed in heavy ion collisions at RHIC. [Copyright &y& Elsevier]

Abstract: We report the STAR measurement of ϕ meson production in and collisions at . Using the event mixing technique, the ϕ spectra and yields are obtained at mid-rapidity for five centrality bins in collisions and for non-singly-diffractive collisions. It is found that the ϕ transverse momentum distributions from collisions are better fitted with a single-exponential while the spectrum is better described by a double-exponential distribution. The measured nuclear modification factors indicate that ϕ production in central collisions is suppressed relative to peripheral collisions when scaled by the number of binary collisions . The systematics of versus centrality and the constant ratio versus beam species, centrality, and collision energy rule out kaon coalescence as the dominant mechanism for ϕ production. [Copyright &y& Elsevier]