Nuclear Spectral Function Research Articles

Low energy kaon photoproduction from nuclei

We study K + -meson production in γA interactions at energies below the reaction threshold in free space. The Thomas–Fermi and spectral function approaches are used for the calculations of the production process. It is found that the measurement of the differential spectra may allow to reconstruct the production mechanism and to investigate the dispersion relations entering the production vertex. It is shown that the contribution from secondary pion induced reactions to the total kaon photoproduction is negligible for E γ<1.2 GeV so that strangeness production at low energies is sensitive to the nuclear spectral function.

Experimental study of the subthreshold production of K +-mesons in proton-nucleus collisions

Energy dependence of the differential cross sections for the production of K +-mesons with a momentum of 1.28 GeV/c (c is the speed of light) by protons incident on Be, Al, Cu, and Ta nuclei was measured for energies both above and below the K +-meson production threshold in pp collisions. Evidence is given for the dominance of the mechanism of direct production in the experiment. The characteristics of momentum distribution are determined for nucleons in the Be and Al nuclei up to 650 MeV/c. The data cannot be described in the model of nuclear spectral function.

On the behavior of the nuclear spectral function at high momentum and removal energy

The extrapolation of the nuclear spectral function at large nucleon three-momentum and removal energy is suggested.

Nuclear effects in the F3 structure function for finite and asymptotic Q2

We study nuclear effects in the structure function F 3 which describes the parity violating part of the charged-current neuitrino nucleon deep inelastic scattering. Starting from a covariant approach we derive a factorized expression for the nuclear structure function in terms of the nuclear spectral function and off-shell nucleon structure functions valid for arbitrary momentum transfer Q and in the limit of weak nuclear binding, i.e. when a nucleus can be treated as a non-relativistic system. We develop a systematic expansion of nuclear structure functions in terms of a Q −2 series caused by nuclear effects (“nuclear twist” series). Basing ourselves on this expansion we calculate nuclear corrections to the Gross-Llewellyn-Smith sum rule as well as to higher moments of F 3. We show that corrections to the GLS sum rule due to nuclear effects cancel out in the Bjorken limit and calculate the corresponding Q −2 correction. Special attention is paid to the discussion of the off-shell effects in the structure functions. A sizable impact of these effects both on the Q 2 and x dependence of nuclear structure functions is found.

Electroinduced two-nucleon knockout and correlations in nuclei

A model to calculate cross sections for electroinduced two-nucleon emission from finite nuclei is presented. Short-range correlations in the wave functions and meson-exchange contributions to the photoabsorption process are implemented. Effects of the short-range correlations are studied with the aid of a perturbation expansion method with various choices of the Jastrow correlation function. The model is used to investigate the relative importance of the different reaction mechanisms contributing to the A(e,e′pn) and A(e,e′pp) process. Representative examples for the target nuclei 12C and 16O and for kinematical conditions accessible with contemporary high-duty cycle electron accelerators are presented. A procedure is outlined to calculate the two-nucleon knockout contribution to the semi-exclusive (e,e′p) cross section. Using this technique we investigate to what extent far semi-exclusive (e,e′p) reactions can be used to detect high-momentum components in the nuclear spectral function.

Multiple hadron production in electron scattering off nuclear targets

We discuss semi-inclusive $\mathrm{eA}\ensuremath{\rightarrow}{e}^{\ensuremath{'}}\mathrm{hX}$ processes in which the hadron $h$ is emitted backward in the rest frame of the target nucleus. The purpose of our analysis is the comparison of two approaches based on different descriptions of nuclear structure at short interparticle distance. The first one uses nucleonic degrees of freedom and a nuclear spectral function obtained from a microscopic many-body calculation, whereas in the second one the relativistic invariant phase-space volume available to a quark in a nucleus is computed, taking into account nucleon-nucleon correlations. The calculated proton and $\ensuremath{\pi}$-meson spectra are compared to the data taken at SLAC using 14.5 GeV ${e}^{+}$ and ${e}^{\ensuremath{-}}$ scattering off CO.

The high momentum and energy behaviour of the nucleon spectral function of nuclear matter within the Brueckner-Bethe-Goldstone approach

Abstract The nuclear single-particle spectral function is considered in the region of high momentum and high removal energy. For these kinematical conditions, far away from the quasi-particle peak, the spectral function is expected to be dominated by nucleon-nucleon correlations. It has been previously argued that the spectral function can be written as a convolution between the two-body relative momentum distribution and the corresponding centre-of-mass distribution of the correlated pairs which characterize the structure of the ground state in this energy-momentum region. It is shown that the convolution model can be microscopically derived from the Brueckner-Bethe-Goldstone (BBG) expansion. At the same time, this result also allows us to establish a direct link between the spectral function and the defect function of the BBG theory. From a numerical comparison with the microscopic spectral function the convolution model turns out to be highly accurate in the relevant momentum and energy range.

Y-SCALING QUANTITIES AND NUCLEON CORRELATION EFFECTS IN NUCLEI

The asymptotic scaling function F(y) and the binding correction B(y), the mean kinetic 〈T〉 and removal 〈E〉 energies, as well as the occupation probabilities Sgr and Sex are calculated in the cases of the 4He, 12C, 16O and 40Ca nuclei using the nucleon momentum distributions obtained within the Jastrow correlation method and the phenomenological model which takes into account short-range and tensor nucleon-nucleon correlations. It is shown that the scaling functions F(y) differ from those obtained in the mean-field approximation but qualitatively agree with the available experimental data. The binding correction B(y) is explicitly evaluated using a model nuclear spectral function. The nucleon-nucleon correlation effects increase the values of the mean kinetic 〈T〉 and mean removal 〈E〉 energies in comparison with their values in the mean-field approximation.

Internal nuclear momentum and subthreshold kaon production

The role of the high momentum component of the nuclear spectral function in subthreshold K + meson production in proton-nucleus collisions is studied. We use the parametrization of the elementary NN → NYK cross section, which is based on the calculations performed with the boson exchange model. The experimental data on quasi-elastic electron and gamma scattering and backward proton production are analyzed in order to extract the high momentum component in nuclei. It is shown that the contribution from the high momentum component to the kaon production is negligible.

Spectral function of medium-heavy nuclei and electron scattering

We calculate the correlated part of the nuclear matter spectral function at various densities employing correlated basis function theory. The correlated part of the spectral function for finite nuclei is obtained from the nuclear matter results by using local density approximation, whereas the mean-field part is extracted from ( e, t′ p) scattering data. The resulting P ( k, E) is used to study inclusive electron scattering at large q; the final state interaction effects are also treated in local density approximation.

Precocious y-scaling and nucleon momentum distributions in nuclei

Recent quasi-elastic electron scattering data on 56Fe are compared with an impulse approximation calculation based on a theoretical nuclear matter spectral function. A y-scaling analysis of the data shows that the scaling limit is approached at lower Q 2 than the theoretical calculation. A new y-scaling analysis based on the properties of the theoretical spectral function is introduced which allows direct comparison of the momentum distribution with the experimental scaling function.

The nuclear spectral function and the mass dependence of the EMC effect

We examine the properties of the nuclear spectral function and point out that the mass dependence of the EMC effect can be reproduced within the conventional nuclear theory by using the appropriate experimental data for the momentum and energy distribution of nucleons in nuclei.