123 research outputs found
Selectivity of the {16}O(e,e'pp) reaction to discrete final states.
No full textResolution of discrete final states in the 16O(e,e'pp)14C reaction may provide an interesting tool to discriminate between contributions from one- and two-body currents in this reaction. This is based on the
observation that the 0+ ground state and first 2+ state of 14C are reached predominantly by the removal of a1S0 pair from 16O in this reaction, whereas other states mostly arise by the removal of a 3P pair. This
theoretical prediction has been supported recently by an analysis of the pair momentum distribution of the experimental data. In this paper we present results of reaction calculations performed in a direct knockout
framework where final-state interaction and one- and two-body currents are included. The two-nucleon overlap integrals are obtained from a calculation of the two-proton spectral function of 16O and include both long-range
and short-range correlations. The kinematics chosen in the calculations is relevant for recent experiments at NIKHEF and Mainz. We find that the knockout of a 3P proton pair is largely due to the two-body Delta current.
The 1S0 pair knockout, on the other hand, is dominated by contributions from the one-body current and therefore sensitive to two-body short-range correlations. This opens up good perspectives for the study of these
correlations in the 16O(e,e'pp) reaction involving the lowest few states in 14C. In particular the longitudinal structure function f 00 , which might be separated with superparallel kinematics, turns out to be quite sensitive
to the NN potential that is adopted in the calculations
Spectroscopic factors in 16O and nucleon asymmetry
No full textThe self-consistent Green's functions method is employed to study the spectroscopic factors of quasiparticle states around 16,28O and 40,60Ca. The Faddeev random phase approximation (FRPA) is used to account for the coupling of particles with collective excitation modes. Results for 16O are reviewed first. The same approach is applied to isotopes with large proton-neutron asymmetry to estimate its effect on spectroscopic factors. The results, based on the chiral N3LO force, exhibit an asymmetry dependence similar to that observed in heavy-ion knockout experiments but weaker in magnitude
Appendix_1 – Supplemental material for Salvage surgery for recurrent or persistent tumour after radical (chemo)radiotherapy for locally advanced non-small cell lung cancer: a systematic review
No full textSupplemental material, Appendix_1 for Salvage surgery for recurrent or persistent tumour after radical (chemo)radiotherapy for locally advanced non-small cell lung cancer: a systematic review by Chris Dickhoff, Rene H. J. Otten, Martijn W. Heymans and Max Dahele in Therapeutic Advances in Medical Oncology</p
Effects of Nuclear Correlations on the 16O(e,e'pN) Reactions to Discrete Final States
No full textCalculations of the 16O(e,e′p N) cross sections to the ground state and first excited levels of the 14C and 14N nuclei are presented. The effects of nuclear fragmentation have been obtained in a self-consistent approach and are accounted for in the determination of the two-nucleon removal amplitudes. The Hilbert space is partitioned in order to compute the contribution of both long- and short-range effects in a separate way. Both the two-proton and the proton-neutron emission cross sections have been computed within the same model for the nuclear structure as well as the same treatment of the reaction mechanism, with the aim of better comparing the differences between the two physical processes. The 16O(e,e′ pp) reaction is found to be sensitive to short-range correlations, in agreement with previous results. The 16O(e,e′ pn) cross section to 1+ final states is dominated by the Δ current and tensor correlations. For both reactions, the interplay between collective (long-range) effects and short-range and tensor correlations plays an important role. This suggests that the selectivity of (e,e′pN) reactions to the final state can be used to probe correlations also beyond short-range effects
Extension of the random phase approximation including the self-consistent coupling to two-phonon contributions
No full textA microscopic formalism is developed that includes the coupling to two particle-hole phonons in the particle-hole propagator by extending the dressed random phase approximation (DRPA) equation for a finite system. The resulting formalism is applied to study the low-lying excitation spectrum of [Formula Presented] It is observed that the coupling to two-phonon states at low energy generates excited states with quantum numbers that cannot be obtained in the DRPA approach. Nevertheless, the two-phonon states mix weakly with particle-hole configurations and participate only partially in the formation of the lowest-lying positive-parity excited states. The stability of the present calculation is tested vs the truncation of model space. It is demonstrated that when single-particle strength fragmentation is properly considered, the present formalism exhibits convergence with respect to the chosen model space within the confines of the chosen approximation scheme
Faddeev treatment of long-range correlations and the one-hole spectral function of O-16
No full textThe Faddeev technique is employed to study the influence of both particle-particle and particle-hole phonons on the one-hole spectral function of 16O. Collective excitations are accounted for at a random phase approximation level and subsequently summed to all orders by the Faddeev equations to obtain the nucleon self-energy. An iterative procedure is applied to investigate the effects of the self-consistent inclusion of the fragmentation in the determination of the phonons and the corresponding self-energy. The present results indicate that the characteristics of hole fragmentation are related to the low-lying states of 16O
Faddeev description of two-hole-one-particle motion and the single-particle spectral function
No full textThe Faddeev technique is employed to address the problem of describing the influence of both particle-particle and particle-hole phonons on the single-particle self-energy. The scope of the few-body Faddeev equations is extended to describe the motion of two-hole-one-particle (two-particle-one-hole) excitations. This formalism allows one to sum both particle-particle and particle-hole phonons, obtained separately in the random phase approximation. The appearance of spurious solutions for the present application of the Faddeev method is related to the inclusion of a consistent set of diagrams. The formalism presented here appears practical for finite nuclei and achieves a simultaneous inclusion of particle-particle and particle-hole phonons to all orders while the spurious solutions are properly eliminated
High-momentum proton removal from 16 O and the (e,e'p) cross section
No full textThe cross section for the removal of high-momentum protons from 16O is calculated for high missing energies. The admixture of high-momentum nucleons in the 16O ground state is obtained by calculating the single-hole spectral function directly in the finite nucleus with the inclusion of short-range and tensor correlations induced by a realistic meson-exchange interaction. The presence of high-momentum nucleons in the transition to final states in 15N at 60¿100 MeV missing energy is converted to the coincidence cross section for the (e,e¿p) reaction by including the coupling to the electromagnetic probe and the final state interactions of the outgoing proton in the same way as in the standard analysis of the experimental data. Detectable cross sections for the removal of a single proton at these high missing energies are obtained which are considerably larger at higher missing momentum than the corresponding cross sections for the p-wave quasihole transitions. Cross sections for these quasihole transitions are compared with the most recent experimental data available
Self-consistent Green's function method for nuclei and nuclear matter
No full textRecent results obtained by applying the method of self-consistent Green's functions to nuclei and nuclear matter are reviewed. Particular attention is given to the description of experimental data obtained from the (e,e′p) and (e,e′2N) reactions that determine one- and two-nucleon removal probabilities in nuclei since the corresponding amplitudes are directly related to the imaginary parts of the single-particle and two-particle propagators. For this reason and the fact that these amplitudes can now be calculated with the inclusion of all the relevant physical processes, it is useful to explore the efficacy of the method of self-consistent Green's functions in describing these experimental data. Results for both finite nuclei and nuclear matter are discussed with particular emphasis on clarifying the role of short-range correlations in determining various experimental quantities. The important role of long-range correlations in determining the structure of low-energy correlations is also documented. For a complete understanding of nuclear phenomena it is therefore essential to include both types of physical correlations. We demonstrate that recent experimental results for these reactions combined with the reported theoretical calculations yield a very clear understanding of the properties of all protons in the nucleus. We propose that this knowledge of the properties of constituent fermions in a correlated many-body system is a unique feature of nuclear physics
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