110 research outputs found
Implications for (d,p) reaction theory from nonlocal dispersive optical model analysis of Ca(d,p)Ca
The nonlocal dispersive optical model (NLDOM) nucleon potentials are used for
the first time in the adiabatic analysis of a (d,p) reaction to generate
distorted waves both in the entrance and exit channels. These potentials were
designed and fitted by Mahzoon [Phys. Rev. Lett. 112, 162502
(2014)] to constrain relevant single-particle physics in a consistent way by
imposing the fundamental properties, such as nonlocality, energy-dependence and
dispersive relations, that follow from the complex nature of nuclei. However,
the NLDOM prediction for the Ca(d,p)Ca cross sections at low
energy, typical for some modern radioactive beam ISOL facilities, is about
70 higher than the experimental data despite being reduced by the NLDOM
spectroscopic factor of 0.73. This overestimation comes most likely either from
insufficient absorption or due to constructive interference between ingoing and
outgoing waves. This indicates strongly that additional physics arising from
many-body effects is missing in the widely used current versions of (d,p)
reaction theories.Comment: 14 pages, 15 figure
Isospin dependence of nucleon Correlations in ground state nuclei
The dispersive optical model (DOM) as presently implemented can investigate
the isospin (nucleon asymmetry) dependence of the Hartree-Fock-like potential
relevant for nucleons near the Fermi energy. Data constraints indicate that a
Lane-type potential adequately describes its asymmetry dependence. Correlations
beyond the mean-field can also be described in this framework, but this
requires an extension that treats the non-locality of the Hartree-Fock-like
potential properly. The DOM has therefore been extended to properly describe
ground-state properties of nuclei as a function of nucleon asymmetry in
addition to standard ingredients like elastic nucleon scattering data and level
structure. Predictions of nucleon correlations at larger nucleon asymmetries
can then be made after data at smaller asymmetries constrain the potentials
that represent the nucleon self-energy. A simple extrapolation for Sn isotopes
generates predictions for increasing correlations of minority protons with
increasing neutron number. Such predictions can be investigated by performing
experiments with exotic beams. The predicted neutron properties for the double
closed-shell 132Sn nucleus exhibit similar correlations as those in 208Pb.
Future relevance of these studies for understanding the properties of all
nucleons, including those with high momentum, and the role of three-body forces
in nuclei are briefly discussed. Such an implementation will require a proper
treatment of the non-locality of the imaginary part of the potentials and a
description of high-momentum nucleons as experimentally constrained by the
(e,e'p) reactions performed at Jefferson Lab.Comment: 7 pages and 7 figure
Microscopic self-energy calculations and dispersive optical-model potentials
Nucleon self-energies for 40Ca, 48Ca, 60Ca isotopes are generated with the
microscopic Faddeev-random-phase approximation (FRPA). These self-energies are
compared with potentials from the dispersive optical model (DOM) that were
obtained from fitting elastic-scattering and bound-state data for 40Ca and
48Ca. The \textit{ab initio} FRPA is capable of explaining many features of the
empirical DOM potentials including their nucleon asymmetry dependence. The
comparison furthermore provides several suggestions to improve the functional
form of the DOM potentials, including among others the exploration of parity
and angular momentum dependence. The non-locality of the FRPA imaginary
self-energy, illustrated by a substantial orbital angular momentum dependence,
suggests that future DOM fits should consider this feature explicitly. The
roles of the nucleon-nucleon tensor force and charge-exchange component in
generating the asymmetry dependence of the FPRA self-energies are explored. The
global features of the FRPA self-energies are not strongly dependent on the
choice of realistic nucleon-nucleon interaction.Comment: Submitted to Phys. Rev.
Transfer reactions and the dispersive optical-model
The dispersive optical-model is applied to transfer reactions. A systematic
study of reactions on closed-shell nuclei using the finite-range
adiabatic reaction model is performed at several beam energies and results are
compared to data as well as to predictions using a standard global
optical-potential. Overall, we find that the dispersive optical-model is able
to describe the angular distributions as well as or better than the global
parameterization. In addition, it also constrains the overlap function.
Spectroscopic factors extracted using the dispersive optical-model are
generally lower than those using standard parameters, exhibit a reduced
dependence on beam energy, and are more in line with results obtained from
measurements.Comment: Phys. Rev. C 84, 044611 (2011
Nonlocal extension of the dispersive-optical-model to describe data below the Fermi energy
Present applications of the dispersive-optical-model analysis are restricted
by the use of a local but energy-dependent version of the generalized
Hartree-Fock potential. This restriction is lifted by the introduction of a
corresponding nonlocal potential without explicit energy dependence. Such a
strategy allows for a complete determination of the nucleon propagator below
the Fermi energy with access to the expectation value of one-body operators
(like the charge density), the one-body density matrix with associated natural
orbits, and complete spectral functions for removal strength. The present
formulation of the dispersive optical model (DOM) therefore allows the use of
elastic electron-scattering data in determining its parameters. Application to
Ca demonstrates that a fit to the charge radius leads to too much
charge near the origin using the conventional assumptions of the functional
form of the DOM. A corresponding incomplete description of high-momentum
components is identified, suggesting that the DOM formulation must be extended
in the future to accommodate such correlations properly. Unlike the local
version, the present nonlocal DOM limits the location of the deeply-bound hole
states to energies that are consistent with (\textit{e,e}\textit{p})
and (\textit{p,2p}) data.Comment: 14 pages, 10 figures, submitted to Physical Review
Microscopic self-energy of Ca from the charge-dependent Bonn potential
The effects of short-range correlations on the nucleon self-energy in
Ca are investigated using the charge-dependent Bonn (CDBonn)
interaction. Comparisons are made with recent results for the self-energy of
Ca derived from the dispersive optical-model (DOM). Particular emphasis
is placed on the non-locality of the imaginary part of the microscopic
self-energy which suggests that future DOM analyses should include this
feature. In particular, data below the Fermi energy appear sensitive to the
implied orbital angular momentum dependence of the self-energy. Quasiparticle
properties obtained for the CDBonn interaction are substantially more
mean-field-like than the corresponding DOM results with spectroscopic factors
larger by about 0.2 e.g. Reaction cross sections obtained from the microscopic
self-energy for scattering energies up to 100 MeV indicate that an adequate
description of volume absorption is obtained while a considerable fraction of
surface absorption is missing. The analysis of the non-locality of the
imaginary part of the microscopic self-energy suggests that a simple gaussian
provides an adequate description, albeit with rather large values for ,
the non-locality parameter.Comment: 18 pages, 19 figures, 4 table
Using the third state of matter: high harmonic generation from liquid targets
High harmonic generation on solid and gaseous targets has been proven to be a powerful platform for the generation of attosecond pulses. Here we demonstrate a novel technique for the XUV generation on a smooth liquid surface target in vacuum, which circumvents the problem of low repetition rate and limited shot numbers associated with solid targets, while it maintains some of its merits. We employed atomically smooth, continuous liquid jets of water, aqueous salt solutions and ethanol that allow uninterrupted high harmonic generation due to the coherent wake emission mechanism for over 8 h. It has been found that the mechanism of plasma generation is very similar to that for smooth solid target surfaces. The vapor pressure around the liquid target in our setup has been found to be very low such that the presence of the gas phase around the liquid jet could be neglected
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