Short-range Correlation Effects Research Articles

Systematic study of the effect of short range correlations on the occupation numbers of the shell model orbits in light nuclei.

The role of short range correlations on the depletion of the Fermi sea is studied in light nuclei. The short range correlations are considered in an approximate treatment allowing a systematic study of nuclei in the region 4{le}{ital A}{le}40. The natural orbital'' representation is used for the determination of the occupation probabilities of the shell model orbits of the ground-state wave function. The depletion of the nuclear Fermi sea appears to be, on the average, about 32%.

Nucleon-nucleon correlation effects in the elastic scattering of alpha particles from 11Li at 26 MeV/nucleon.

The cross section for the elastic scattering of {alpha} particles from {sup 11}Li at {ital E}{sub lab}=26 MeV/nucleon is calculated. The single-folding potential plus second-order rescattering correction is used as an optical potential. It is found that the angular distribution is farside dominated. The second-order correction, which contains the short-range correlation effects, merely adds to absorption. Comparison to the {alpha}+{sup 12}C system is made.

Spectral functions and momentum distribution of fully polarized liquid 3He.

We study the effects of short-range correlations on single-particle properties in fully spin-polarized liquid {sup 3}He ({sup 3}He{sup {up arrow}}). By calculating the full frequency dependence of the self-energy, we are able to obtain the spectral functions, quasiparticle strength, momentum distribution, {omega} mass, and {ital k} mass. We start from the He-He interatomic potential and use the Galitskii-Feynman-Hartree-Fock (GFHF) approximation for the self-energy. In the GFHF approximation, the vertex is represented by the Galitskii-Feynman {ital T} matrix, which includes particle-particle and hole-hole scattering to all orders, and thus is a good representation of the short-range correlation effects brought about by the strong core repulsion of the He-He potential. We find large departures from independent-particle behavior, indicating that the system is highly correlated. In particular, we find that the quasiparticle pole takes up only about 50% of the strength of the spectral functions for a wide range of momenta near {ital k}{sub {ital F}}. There is a substantial depletion of the occupation of states within the Fermi sea, the {ital k}=0 state being only 83% occupied. We comment on the relevance of these results for a description of neutron scattering from normal {sup 3}He. Approximations for the ground-state energy are investigated.

Low-energy positron-H2 collisions in the distributed positron model

A new treatment of short-range correlation effects (the distributed positron model) is used to calculate a variety of scattering results for low-energy positrons on H2. The new treatment of correlation is based on a physically motivated approximation that mimics the effect of virtual positronium formation, but requires no semiempirical parameters or non-physical assumptions. The author's total, integrated cross sections are found to be in excellent agreement with measured values. The differential cross sections and eigenphase sums are compared with the results of several recent ab initio calculations.

Effects of short-range correlations on the self-energy in the optical model of finite nuclei

The real and imaginary parts for the self-energy of a nucleon interacting with a finite nucleus ( 16O) are derived from a realistic one-boson-exchange potential including terms up to second order in the Brueckner G-matrix. Effects of 2-particle-1-hole and 3-particle-2-hole correlations on the optical model potential are evaluated. The studies are performed in a mixed representation, employing a basis of oscillator functions for the occupied hole states and plane wave states for the unoccupied particle states. Attempts are discussed to represent the resulting self-energies in terms of a local energy-dependent potential.

Electron scattering from krypton atoms between 1-20 eV

Differential, integral and momentum transfer cross sections are reported for electron-Kr collisions in the range 1-20eV. An optical potential approach is employed; the static potential is included exactly at the Hartree-Fock level, the short-range correlation and long-range polarisation effects are considered in density functional theory. For exchange interection, we tune the free-electron-gas-exchange (FEGE) potential with respect to R-matrix integral cross section at 1 eV. The tuning parameter is the ionization potential of the atom. The tuned FEGE approximation at 1 eV gives very good results on the differential and integral cross sections at all energies between 1-20eV as compared with recent measurements and the R-matrix calculations. We also discuss the range of validity of the present tuned potential.

Collision strengths for electron impact excitation of Cl IX from its ground state

The R-matrix method is used to calculate collision strengths for electron impact excitation of Cl IX from its ground state (2P0). Configuration interaction wavefunctions are used to represent twelve target states which are included in the calculations. Finally the effective collision strengths have been calculated for electron temperatures in the range (5*103-105) by assuming a Maxwellian electron velocity distribution for the incident electrons. This is the first detailed calculation on this ion in which the effects of exchange, channel couplings and short-range correlation effects are taken into account.

Effects of short-range correlations and three-body force on proton-3He scattering at high energy

Proton-3He elastic scattering is studied within the framework of the Glauber approximation at 1 GeV. The short-range correlations and the three-body force effects are studied. These effects are considered through a ground state wavefunction of the target nucleus. The results are discussed and compared with experimental data.

A Bound on the Majoron Coupling to the Neutrino

The nuclear neutrinoless double beta decay with emission of a Majoron is discussed by means of a diagrammatic effective operator approach. In the calculation, the effects of the nuclear short range correlation and nuclear core polarization have been taken into account. The effective Majoron coupling to neutrino is then deduced from the experimental half-life of 48Ca double beta decay with the result ⟨gH0⟩ < (2 ∼ 3) × 10-4.

Theory of hopping rate of localized charged particles in metals: Electron scattering.

The hopping rate of localized charged particles in metals is studied. The density-density correlation function is calculated in the presence of electron-electron interactions. The equation-of-motion method is used to calculate the two-particle Green's function. Explicit results for correlation functions are obtained within the generalized random-phase approximation. The Coulomb repulsion between electrons is represented by an effective potential, which takes account of short-range correlation effects. We found that the hopping rate is greatly reduced by electronic virtual excitations. Unlike previous theories, our calculations show that both particle-hole and plasmon excitations contribute to the renormalization of the tunneling matrix. It is shown that electron correlations effectively reduce the hopping rate at low temperatures. It is also shown that the effect of dynamic screening increases the hopping rate. Calculation shows that the reduction due to plasmon excitation can be as large as one to two orders of magnitude in normal metals.

Low-density electron liquid.

We present an exchange-antisymmetric calculation of the particle-hole interaction in the low-density electron liquid. Long-range screening of the Coulomb interaction is incorporated in a self-consistent manner, and we discuss the general method of incorporating screening, both long range and short range, within this framework. The scattering amplitude is separated into a short-range direct part and a long-range induced interaction. The short-range part includes the effects of short-range electron-electron correlations phenomenologically via polarization potentials. The long-range piece arises from the exchange of particle-hole excitations. These particle-hole excitations provide the screening of the bare Coulomb interaction in the q\ensuremath{\rightarrow}0 limit.

Beyond the plane-wave impulse approximation in (e,e'p) reactions.

The orthonormal-correlated-states method is used to study the $^{4}\mathrm{He}$(e,e'p${)}^{3}$H reaction. The effects of short-range correlations, orthogonality corrections, p${+}^{3}$H interaction in the final states, and two-body charge and current operators bring the theoretical predictions into fair agreement with the NIKHEF and Saclay data.

Multiple light scattering from concentrated, interacting suspensions.

The effects of short-range interparticle correlations on the multiple scattering of light in colloidal suspensions are studied. Our measurements, and comparisons with theory, of the transport mean free path and the width of the coherent backscattering cone demonstrate the validity of the diffusion approximation of light in correlated suspensions. Dynamic multiple-light-scattering measurements allow determination of the short-time self-diffusion constant of the spheres. The data agree with hydrodynamic theory up to 45% volume fraction with no adjustable parameters.

The role of nucleon-nucleon short-range correlations in the nuclear structure function in thex &gt; 1 region

By using the Jastrow correlation wave function, the role of nucleon-nucleon short-range correlations in the nuclear structure function in thex > 1 region is reanalyzed. The result shows that, with the proper energy-momentum distribution of nucleons in the nucleus including the effect of nucleon-nucleon short-range correlations, the experimental data of the nuclear structure function in thex > 1 region can not be well explained. It seems that additional components which go beyond the conventional nuclear physics are necessary to describe the effect.

A modified adiabatic approach to positron-atom and positron-molecule polarisation potentials: application to positron-He scattering

A novel treatment of short-range correlation effects designed for use in calculating positron-atom and positron-molecule polarisation potentials is presented. The treatment is based on a physically motivated approximation that mimics the effect of the dominant non-adiabatic correction to the adiabatic potential at low scattering energies, namely virtual positronium formation. As an initial test of the method, positron-He scattering phaseshifts, scattering length and differential cross sections have been calculated and found to be in good agreement with accurate results. This method is immediately extendible to positron-molecule collisions and does not require significantly more work than a purely adiabatic treatment.

SHORT RANGE CORRELATIONS AND NUCLEON EMISSION IN PERIPHERAL RELATIVISTIC HEAVY ION COLLISIONS

We investigate the effects of short range correlations on nucleon emission in peripheral relativistic heavy ion collisions, following an idea originally proposed by Feshbach and Zabek. Expressions for one- and two-nucleon emission cross sections are derived and calculations for typical heavy ion systems are performed. We show that momentum conservation in the phonon absorption process leads to pronounced ridges in the quadruple-differential cross section for two-nucleon emission. We suggest that the presence of such ridges in future exclusive experiments should be considered as a signature of correlated emission of a nucleon pair.

14C( pi +, pi -)14O reaction between 19 and 80 MeV.

Cross-section measurements are reported for the /sup 14/C(..pi../sup +/,..pi../sup /minus//)/sup 14/O reaction to the double isobaric analog state and for nonanalog states at 5 to 10 MeV excitation. The extrapolated zero-degree cross sections are 2.3+-0.5, 3.7+-0.4, 2.2+-0.3, and 0.9+-0.3 ..mu..b/sr at 19.0, 29.1, 64.4, and 79.5 MeV, respectively. The nonanalog-state cross sections are found to rise sharply with increasing beam energy above 50 MeV, in contrast to those of the double isobaric analog state transition. Calculations with a phenomenological isospin-dependent optical potential must include an isotensor term, which accounts for transitions through nonanalog intermediate states or other short-range correlations, in order to describe the energy and angular trends of the data. Microscopic calculations in the second-order distorted-wave impulse approximation fail to reproduce the cross sections near 50 MeV unless the effects of short-range correlations beyond those contained in the model are incorporated.

A simple description of nucleon high-momentum components due to short-range correlations in nuclei

Effects of short-range correlations are included in nuclear momentum distribution also using a simple method suitable for high mass number nuclei.

High-energy photons in neutron-proton and proton-nucleus collisions.

In an effort to better understand the dynamics of nucleon-nucleon bremsstrahlung in producing energetic photons, we have investigated the contribution of each part of the current associated with the different terms in the nuclear Hamiltonian to the neutron-proton bremsstrahlung cross sections. In the range of photon energy investigated here, we find meson-exchange currents to be the dominant source of high-energy photons (\ensuremath{\omega}\ensuremath{\gtrsim}50 MeV). Although the one-body current contribution is small for such energetic photons, its interference with the two-body current is important and enhances the cross section. At low photon energy the convection current dominates. We find that the bremsstrahlung cross section is very sensitive to the $^{3}$(SD${)}_{1}$ states and offers a potential means of investigating short-range correlation effects. Off-energy-shell effects are estimated to have only a small influence on the neutron-proton bremsstrahlung inclusive cross section. In connection with the neutron-proton bremsstrahlung process, the nucleon-nucleon collisional mechanism in producing high-energy photons in proton-induced reactions has been also investigated within the nuclear matter approximation. Nuclear medium effects in intermediate states are shown to have a minor influence on the photon cross section; therefore, the use of a free nucleon-nucleon T matrix instead of a G matrix seems to be well justified. However, the results are found to be very sensitive to medium effects in the initial and final states.

Longitudinal and transverse response functions of three-body nuclei

The method of correlated orthogonal states is used to study the longitudinal and transverse response of 3He and 3H. The treatment of the d + N final states is improved by including a real d-N optical potential. The effects of short range correlations, orthogonality corrections, and d-N interaction in the final states bring the theoretical 3He longitudinal and transverse, and 3H transverse response functions into reasonable agreement with experiment, although a systematic lack of strength persists in the calculated 3H longitudinal response at low ω.