Searcharxiv⌕ Search

arXiv subjects

E. M. Darwish

Publications and source records attributed to E. M. Darwish.

9 recordsLinked to original sources
arXiv2026

Tensor analyzing power $T_{20}$ in the reaction $γ\vec{d}\to pn$ at photon energies 350-680 MeV

We present measurements of the tensor analyzing power $T_{20}$ in the reaction $γ{d}\to pn$ at photon energies $E_γ= 350$-$680$~MeV. The experiment was performed at the VEPP-3 storage ring using an internal tensor-polarized deuterium gas target and a tagged quasi-real photon beam. The data were obtained for proton emission angles $Θ_p = 70^\circ$-$102^\circ$. Comparison with modern meson-baryon calculations shows generally satisfactory agreement within the present uncertainties. A theoretical analysis of an extended data set, covering the energy range from threshold to 680~MeV and including both the new data and the previous results from 2007, is presented.

nucl-ex↗
arXiv2004

Single-spin asymmetries of $d(γ,π)NN$ in the first resonance region

Incoherent photoproduction of pions on the deuteron in the first resonance region is investigated with special emphasis on single-spin asymmetries. For the elementary pion production operator an effective Lagrangian model which includes the standard pseudovector Born terms and a resonance contribution from the $Δ$(1232)-excitation is used. Single-spin asymmetries, both for charged and neutral pion photoproduction on the deuteron, are analyzed and calculated for the first time in the first resonance region. The linear photon asymmetry $Σ$, vector target asymmetry $T_{11}$ and tensor target asymmetries $T_{20}$, $T_{21}$, and $T_{22}$ for the reaction $d(γ,π)NN$ are predicted for forthcoming experiments.

nucl-th↗
arXiv2003

Self-consistent treatment of the self-energy in nuclear matter

The influence of hole-hole propagation in addition to the conventional particle-particle propagation, on the energy per nucleon and the momentum distribution is investigated. The results are compared to the Brueckner-Hartree-Fock (BHF) calculations with a continuous choice and conventional choice for the single-particle spectrum. The Bethe-Goldstone equation has been solved using realistic $NN$ interactions. Also, the structure of nucleon self-energy in nuclear matter is evaluated. All the self-energies are calculated self-consistently. Starting from the BHF approximation without the usual angle-average approximation, the effects of hole-hole contributions and a self-consistent treatment within the framework of the Green function approach are investigated. Using the self-consistent self-energy, the hole and particle self-consistent spectral functions including the particle-particle and hole-hole ladder contributions in nuclear matter are calculated using realistic $NN$ interactions. We found that, the difference in binding energy between both results, i.e. BHF and self-consistent Green function, is not large. This explains why is the BHF ignored the 2h1p contribution.

nucl-th↗
arXiv2003

Polarization observables in the $γd\toπNN$ reaction in the $Δ$(1232)-resonance region

Incoherent pion photoproduction on the deuteron in the $Δ$(1232)-resonance region is investigated with special emphasis on polarization observables. For the elementary pion photoproduction operator an effective Lagrangian model which includes the standard pseudovector Born terms and a resonance contribution from the $Δ$(1232)-excitation is used. Our results for the elementary $γN\toπN$ reaction are in good agreement with recent experimental data and results of other theoretical calculations. A general analysis of all possible polarization observables for the $γd \toπNN$ reaction with polarized photon beam and/or oriented deuteron target is presented. The unpolarized differential cross section, photon asymmetry, vector and tensor target asymmetries are predicted for forthcoming experiments.

nucl-th↗
arXiv2003

Extracting a value of the slope of the neutron form factor $G_{En}(q^2)$ at $q^2=0$ by reanalysis of the experimental data

A new value $b=0.0205\pm0.0017$ fm$^2$ of the slope of the neutron form factor $G_{En}(q^2)$ at $q^2=0$ compatible with deuteron properties has been extracted by using a linear relation between $b$ and $A^2_S(1+η^2)$ we found for a class of nonlocal potential models having the experimental values of both $r_D$ and $Q$. Another {\it model dependent} value $b^{\rm MHKZ}=0.0206\pm0.0014$ fm$^2$, which is also compatible with deuteron properties, has been determined by applying "constrained" unitary transformations to the local MHKZ potential model. The sensitivity of a small changes in the experimental values used for $r_D$ and $Q$ on the value obtained for $b$ is also investigated.

nucl-th↗
arXiv2003

Final state interaction in spin asymmetry and GDH sum rule for incoherent pion production on the deuteron

The contribution of incoherent single pion photoproduction to the spin response of the deuteron, i.e., the asymmetry of the total photoabsorption cross section with respect to parallel and antiparallel spins of photon and deuteron, is calculated over the region of the $Δ$-resonance with inclusion of final state $NN$- and $πN$-rescattering. Sizeable effects, mainly from $NN$-rescattering, are found leading to an appreciable reduction of the spin asymmetry. Furthermore, the contribution to the Gerasimov-Drell-Hearn integral is explicitly evaluated by integration up to a photon energy of 550 MeV. Final state interaction reduces the value of the integral to about half of the value obtained for the pure impulse approximation.

nucl-th↗
arXiv2002

Present status of electromagnetic reactions on the deuteron above pion threshold

The present status of the theoretical description of electromagnetic reactions on the deuteron above pion threshold is reviewed. Three major topics are considered: (i) retardation effects in $π$-meson exchange contributions to $NN$-interaction and meson exchange currents in deuteron photodisintegration above $π$-threshold in the $Δ$-resonance region, (ii) off-shell effects in the one-body current treated in a simple pion cloud model in deuteron photodisintegration in and above the $Δ$-resonance region, and (iii) final state interaction effects in photoproduction of $π$ and $η$ mesons on the deuteron.

nucl-th↗
arXiv2002

Influence of final state interaction on incoherent pion photoproduction on the deuteron in the region of the Delta-resonance

The influence of final state $NN$- and pi N-rescattering in incoherent pion photoproduction on the deuteron has been investigated. For the elementary photoproduction operator an effective Lagrangian model is used which describes well the elementary reaction. The interactions in the final two-body subsystems are taken in separable form. While NN-rescattering shows quite a significant effect, particularly strong for neutral pion production, pi N-rescattering is almost negligible. Inclusion of such effects leads to an improved and quite satisfactory agreement with experiment.

nucl-th↗