134 research outputs found
A New Approach to y-scaling and the Universal Features of Scaling Functions and Nucleon Momentum Distributions
Some systematic general features of y-scaling structure functions, which are
essentially independent of detailed dynamics, are pointed out. Their physical
interpretation in terms of general characteristics, such as a mean field
description and nucleon-nucleon correlations, is given and their relationship
to the momentum distributions illustrated. A new relativistic scaling variable
is proposed which incorporates the momentum dependence of the excitation energy
of the (A-1) system, with the resulting scaling function being closely related
to the longitudinal momemtum distributions and being free from removal-energy
scaling violating effects.Comment: 17 pages, RevTeX, 4 ps Figures, to appear in Physics Letters
State-dependent Jastrow correlation functions for 4He nuclei
We calculate the ground-state energy for the nucleus 4He with V4 nucleon
interactions, making use of a Jastrow description of the corresponding
wavefunction with state-dependent correlation factors. The effect related to
the state dependence of the correlation is quite important, lowering the upper
bound for the ground-state energy by some 2 MeV.Comment: 10 pages, REVTeX, to be published in J. Phys. G: Nucl. Part. Phy
Universal pattern in (e,e'p) at large missing momenta: quasi-deuteron or diffractive final state interactions?
The intrinsic single particle momentum distributions in nuclei are supposed
to show a universal behavior at large momenta, dominated by short-range
correlated pairs, or quasi-deuterons. We discuss whether the quasi-deuteron
universality survives the final state interaction effects, which are present in
the missing momentum spectra measured in experiments at GeV
energies. We demonstrate that in the observed missing momentum spectra an
approximate universality is present, but originating from the universal pattern
of diffractive final state interactions of the struck proton independent of the
target nucleus.Comment: 10 pages, Latex, 3 uuencoded figure
A unitary correlation operator method
The short range repulsion between nucleons is treated by a unitary
correlation operator which shifts the nucleons away from each other whenever
their uncorrelated positions are within the replusive core. By formulating the
correlation as a transformation of the relative distance between particle
pairs, general analytic expressions for the correlated wave functions and
correlated operators are given. The decomposition of correlated operators into
irreducible n-body operators is discussed. The one- and two-body-irreducible
parts are worked out explicitly and the contribution of three-body correlations
is estimated to check convergence. Ground state energies of nuclei up to mass
number A=48 are calculated with a spin-isospin-dependent potential and single
Slater determinants as uncorrelated states. They show that the deduced energy-
and mass-number-independent correlated two-body Hamiltonian reproduces all
"exact" many-body calculations surprisingly well.Comment: 43 pages, several postscript figures, uses 'epsfig.cls'. Submitted to
Nucl. Phys. A. More information available at http://www.gsi.de/~fm
Stressed backbone and elasticity of random central-force systems
We use a new algorithm to find the stress-carrying backbone of ``generic''
site-diluted triangular lattices of up to 10^6 sites. Generic lattices can be
made by randomly displacing the sites of a regular lattice. The percolation
threshold is Pc=0.6975 +/- 0.0003, the correlation length exponent \nu =1.16
+/- 0.03 and the fractal dimension of the backbone Db=1.78 +/- 0.02. The number
of ``critical bonds'' (if you remove them rigidity is lost) on the backbone
scales as L^{x}, with x=0.85 +/- 0.05. The Young's modulus is also calculated.Comment: 5 pages, 5 figures, uses epsfi
The Single-Particle Spectral Function of
The influence of short-range correlations on the -wave single-particle
spectral function in is studied as a function of energy. This
influence, which is represented by the admixture of high-momentum components,
is found to be small in the -shell quasihole wave functions. It is therefore
unlikely that studies of quasihole momentum distributions using the
reaction will reveal a significant contribution of high momentum components.
Instead, high-momentum components become increasingly more dominant at higher
excitation energy. The above observations are consistent with the energy
distribution of high-momentum components in nuclear matter.Comment: 5 pages, RevTeX, 3 figure
State Dependent Effective Interaction for the Hyperspherical Formalism
The method of effective interaction, traditionally used in the framework of
an harmonic oscillator basis, is applied to the hyperspherical formalism of
few-body nuclei (A=3-6). The separation of the hyperradial part leads to a
state dependent effective potential. Undesirable features of the harmonic
oscillator approach associated with the introduction of a spurious confining
potential are avoided. It is shown that with the present method one obtains an
enormous improvement of the convergence of the hyperspherical harmonics series
in calculating ground state properties, excitation energies and transitions to
continuum states.Comment: LaTeX, 16 pages, 8 ps figure
Translationally invariant treatment of pair correlations in nuclei: I. Spin and isospin dependent correlations
We study the extension of our translationally invariant treatment of few-body nuclear systems to heavier nuclei. At the same time we also introduce state-dependent correlation operators. Our techniques are tailored to those nuclei that can be dealt with in LS coupling, which includes all nuclei up to the shell closure at A=40. We study mainly p-shell nuclei in this paper. A detailed comparison with other microscopic many-body approaches is made, using a variety of schematic nuclear interactions. It is shown that our methodology produces very good energies, and presumably also wave functions, for medium mass nuclei
Do final state interactions obscure short range correlation effects in quasielastic scattering?
Are short range correlations in the ground state of the target nucleus
(initial state correlations ISC)observable inexperiments on quasielastic
scattering at large missing momentum ? Will the missing
momentum spectrum observed at CEBAF be overwhelmed by final state interactions
of the struck proton? Taking the nucleus with a realistic model wave
function for a testing ground, we present a full calculation of the missing
momentum distribution in inclusive scattering. We find a
complex interplay and strong quantum-mechanical interference of FSI and ISC
contributions to scattering at large , with drastic change of the
interference pattern from the (anti)parallel to transverse kinematics. We show
that in all the kinematical conditions, for missing momenta p_{m}\gsim
1\,fm, quasielastic scattering is dominated by FSI effects and the
sensitivity to details of the nuclear ground state is lost. The origin of the
FSI dominance is well understood and can be traced back to the anisotropic
behaviour of FSI which is long ranged in the longitudinal direction and short
ranged in the transverse direction in the opposite to the short ranged ground
state correlations
Two-Body Correlations in Nuclear Systems
Correlations in the nuclear wave-function beyond the mean-field or
Hartree-Fock approximation are very important to describe basic properties of
nuclear structure. Various approaches to account for such correlations are
described and compared to each other. This includes the hole-line expansion,
the coupled cluster or ``exponential S'' approach, the self-consistent
evaluation of Greens functions, variational approaches using correlated basis
functions and recent developments employing quantum Monte-Carlo techniques.
Details of these correlations are explored and their sensitivity to the
underlying nucleon-nucleon interaction. Special attention is paid to the
attempts to investigate these correlations in exclusive nucleon knock-out
experiments induced by electron scattering. Another important issue of nuclear
structure physics is the role of relativistic effects as contained in
phenomenological mean field models. The sensitivity of various nuclear
structure observables on these relativistic features are investigated. The
report includes the discussion of nuclear matter as well as finite nuclei.Comment: Review, 104 pages including figure
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