Bassam A. Shehadeh | Searcharxiv

arXiv2026

Nucleon Nucleon Potential Using N$3$LO Chiral Effective Field Theory

A microscopic description of nucleon-nucleon (NN) and nucleon-nucleus (NA) scattering is developed using chiral effective field theory (chiEFT) at next-to-next-to-next-to-leading order N3LO. The NN interaction is taken from the EGM formulation, which incorporates spectral function regularization Lambda-tilde to control short range components of the two pion exchange force, together with a Gaussian regulator Lambda to ensure convergence of the Lippmann-Schwinger (LS) equation. The regulator parameters (Lambda, Lambda-tilde) = (450, 500), (550, 600), (600, 600) MeV. The resulting chiEFT NN t-matrix is used to construct the first order optical potential, from which Wolfenstein amplitudes and elastic differential cross sections are calculated. The theoretical amplitudes (B) and (C) for pp and pn scattering at 100 and 200 MeV show good overall agreement with experimental data, with the largest discrepancies appearing in the small real component of the spin orbit amplitude. Calculations of p + 16O and p + 40Ca elastic scattering at 100 and 200 MeV reproduce the measured angular distributions with high accuracy, particularly at forward and intermediate angles. These results demonstrate that the EGM chiEFT potential provides a consistent and quantitatively reliable framework for describing NN observables and NA elastic scattering in the 100-200 MeV energy range, while highlighting the need for improved treatment of short range and spin dependent contributions at higher energies.

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arXiv2022

Review of Gamow-Teller and Fermi Transition Strength Functions

We studied the temperature effect in isospin-singlet pairings in Gamow-Teller excitations. We use theories of a hole-particle in the mean field shell model studied decay transition using the one-particle-one-hole model for the $β$-decay of odd-even isotopes and the two-particle-hole models for the $β$-decay of even-even and/or odd-odd isotopes. Our reference isotopes for the one-particle-one-hole model are \ce{^{15}O}, \ce{^{15}N}, \ce{^{17}F}, and \ce{^{41}Sc}, whereas for the two-particle-hole model we use \ce{^{16}N} (for $β^-$-decay) and \ce{^{56}Ni} and \ce{^{40}Sc} (for $β^+$/EC). The calculations involve evaluating the matrix elements of Gamow -Teller and Fermi transitions, then calculate the reduced transition probabilities of Gamow-Teller and Fermi, from which we evaluate the half-lives and the strength function $ft$. The results are compared with the available experimental data. For one-particle-one-hole model we found there is a deviation from experimental values which indicates that the model is not valid for beta decay for the even-even nuclei in the ground state due to the residual nucleon-nucleon interaction. As for a two-particle-hole model, we calculated the transition amplitude, from which we calculated the strength of the transition $\log ft$ values. We found an excellent agreement between experimental and theoretical results. By drawing the relationship between temperature versus $\log ft$ values, we found the general trend is that the strength function values slowly decrease as temperatures increases. There are fluctuations $\log ft$ due to the strongly dependent of $\log ft$ on the shell configuration of the valence nucleons.

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