Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMicroscopic Optical Potential for Elastic Proton-Nucleus Scattering from Chiral Forces
71
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
A microscopic optical potential (OP) is derived from NN chiral potentials at the first-order term within the spectator expansion of the multiple scattering theory and adopting the impulse approximation. The performances of our OP are compared with those of a phenomenological OP in the description of elastic proton scattering data on different isotopic chains. An analogous scheme is adopted to construct a microscopic OP for elastic antiproton-nucleus scattering. The results of our OPs are in reasonably good agreement with the experimental data, for both elastic proton and antiproton-nucleus scattering.
rate research
Read More
The energy- and density-dependent single-particle potential for nucleons is constructed in a medium of infinite isospin-symmetric nuclear matter starting from realistic nuclear interactions derived within the framework of chiral effective field theory. The leading-order terms from both two- and three-nucleon forces give rise to real, energy-independent contributions to the nucleon self-energy. The Hartree-Fock contribution from the two-nucleon force is attractive and strongly momentum dependent, in contrast to the contribution from the three-nucleon force which provides a nearly constant repulsive mean field that grows approximately linearly with the nuclear density. Together, the leading-order perturbative contributions yield an attractive single-particle potential that is however too weak compared to phenomenology. Second-order contributions from two- and three-body forces then provide the additional attraction required to reach the phenomenological depth. The imaginary part of the optical potential, which is positive (negative) for momenta below (above) the Fermi momentum, arises at second-order and is nearly inversion-symmetric about the Fermi surface when two-nucleon interactions alone are present. The imaginary part is strongly absorptive and requires the inclusion of an effective mass correction as well as self-consistent single-particle energies to attain qualitative agreement with phenomenology.
We investigate the effects of chiral three-nucleon force (3NF) on proton scattering at 65 MeV and $^{4}$He scattering at 72 MeV/nucleon from heavier targets, using the standard microscopic framework composed of the Brueckner-Hartree-Fock (BHF) method and the $g$-matrix folding model. For nuclear matter, the $g$ matrix is evaluated from chiral two-nucleon force (2NF) of N$^{3}$LO and chiral 3NF of NNLO by using the BHF method. Since the $g$ matrix thus obtained is numerical and nonlocal, an optimum local form is determined from the on-shell and near-on-shell components of $g$ matrix that are important for elastic scattering. For elastic scattering, the optical potentials are calculated by folding the local chiral $g$ matrix with projectile and target densities. This microscopic framework reproduces the experimental data without introducing any adjustable parameter. Chiral-3NF effects are small for proton scattering, but sizable for $^{4}$He scattering at middle angles where the data are available. Chiral 3NF, mainly in the 2$pi$-exchange diagram, makes the folding potential less attractive and more absorptive for all the scattering.
We formulate microscopic optical potentials for nucleon-nucleus scattering from chiral two- and three-nucleon forces. The real and imaginary central terms of the optical potentials are obtained from the nucleon self energy in infinite nuclear matter at a given density and isospin asymmetry, calculated self-consistently to second order in many-body perturbation theory. The real spin-orbit term is extracted from the same chiral potential using an improved density matrix expansion. The density-dependent optical potential is then folded with the nuclear density distributions of 40Ca, 42Ca, 44Ca, and 48Ca from which we study proton-nucleus elastic scattering and total reaction cross sections using the reaction code TALYS. We compare the results of the microscopic calculations to those of phenomenological models and experimental data up to projectile energies of E = 180 MeV. While overall satisfactory agreement with the available experimental data is obtained, we find that the elastic scattering and total reaction cross sections can be significantly improved with a weaker imaginary optical potential, particularly for larger projectile energies.
Information on the equation of state (EOS) of neutron matter may be gained from studies of 208Pb. Descriptions of 208Pb require credible models of structure, taking particular note also of the spectrum. Such may be tested by analyses of scattering data. Herein, we report on such analyses using an RPA model for 208Pb in a folding model of the scattering. No a posteriori adjustment of parameters are needed to obtain excellent agreement with data. From those analyses, the skin thickness of 208Pb is constrained to lie in the range 0.13-0.17 fm.
We compute the isospin-asymmetry dependence of microscopic optical model potentials from realistic chiral two- and three-body interactions over a range of resolution scales $Lambda simeq 400-500$,MeV. We show that at moderate projectile energies, $E_{rm inv} = 110 - 200$,MeV, the real isovector part of the optical potential changes sign, a phenomenon referred to as isospin inversion. We also extract the strength and energy dependence of the imaginary isovector optical potential and find no evidence for an analogous phenomenon over the range of energies, $E leq 200$,MeV, considered in the present work. Finally, we compute for the first time the leading corrections to the Lane parametrization for the isospin-asymmetry dependence of the optical potential and observe an enhanced importance at low scattering energies.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
