Influence of final state interaction on incoherent η-photoproduction on the deuteron near threshold*

Incoherent η-photoproduction on the deuteron is studied for photon energies from threshold up to 720 MeV. The elementary γN → ghN amplitude is constructed in the frame of a conventional isobar model. Effects of final state interaction are investigated and their role in the cross section as well as in polarization observables is found to be important. Inclusion of such effects leads to a satisfactory agreement with experimental data in the near threshold region. In addition, recent experimental results on the coherent reaction d(γ, gh)d are discussed.     

πphotoproduction on the deuteron via Δ-excitation using the Lorentz Integral Transform

The Lorentz Integral Transform method (LIT) is extended to pion photoproduction in the Δ-resonance region. The main focus lies on the solution of the conceptual difficulties which arise if energy-dependent operators for nucleon resonance excitations are considered. In order to demonstrate the applicability of our approach, we calculate the inclusive cross-section for π⁰-photoproduction off the deuteron within a simple pure resonance model.     

General survey of polarization observables in deuteron electrodisintegration

Polarization observables in inclusive and exclusive electrodisintegration of the deuteron using a polarized beam and an oriented target are systematically surveyed using the standard nonrelativistic framework of nuclear theory but with leading-order relativistic contributions included. The structure functions and the asymmetries corresponding to the various nucleon polarization components are studied in a variety of kinematic regions with respect to their sensitivity to realistic NN-potential models, to subnuclear degrees of freedom in terms of meson exchange currents, isobar configurations and to relativistic effects in different kinematical regions, serving as a benchmark for a test of present standard nuclear theory with effective degrees of freedom.     

Treatment of the Δ current in electromagnetic two-nucleon knockout reactions

The contribution of the Δ(1232) isobar to the electromagnetic current of the two-nucleon system and its role in (γ,NN) processes is investigated. The difference between the genuine Δ-excitation current and that part of the current connected to the deexcitation of a preformed Δ in the target nucleus is stressed. The latter cannot lead to a resonant behaviour of matrix elements for energies in the Δ region. The reaction ¹⁶O(γ, pp)¹⁴C, where the Δ contribution is dominant at intermediate energies, is considered. The large variations found in the cross sections for different treatments stress the need for a proper treatment of the Δ current for a clear understanding of the reaction mechanism of two-nucleon emission processes.     

Consistent treatment of relativistic corrections in deuteron photodisintegration in a one-pion-exchange model

Using a one-pion-exchange model for the nucleon-nucleon interaction the relativistic corrections to potential and to the electromagnetic operators are derived in a power expansion of (p/M). All corrections up to the order (p/M)³ are consistently included. Numerical results are shown for differential cross section and polarization observables for deuteron photodisintegration. A sizeable influence of relativistic effects on some observables is found even at low energies. A comparison of our operators with the expressions of other authors is given.Supported by Deutsche Forschungsgemeinschaft (SFB 201)     

Exchange effects in photon scattering off the deuteron

Detailed calculations of elastic photon-deuteron scattering cross sections for photon energies up to about the π-production threshold are presented. The scattering amplitude is decomposed into scalar, vector and tensor polarizabilities for the various electric and magnetic multipole combinations. This includes a general multipole expansion of the two-photon operator. The imaginary part of the polarizabilities is determined from the contribution to the total cross section using the optical theorem. The real part is then obtained from dispersion relations. Special emphasis is laid on the discussion of exchange effects for both the resonance and the two-photon amplitude. These affect strongly the resonance amplitude whereas for the two-photon amplitude we find only a small effect beyond the important low-energy limit. Another important result is the large vector polarizability at higher energies related to the optical activity of the deuteron.     

Deuteron photodisintegration at low energies

All presently available experimental data on deuteron photodisintegration below 40 MeV (i.e., total and differential cross sections, photon asymmetry and neutron polarization) are collected and carefully compared with the present status of the conventional theory (i.e., in the framework of mesontheoretical or semi-phenomenologicalN-N potentials including subnuclear degrees of freedom and relativistic corrections). No significant evidence for a failure of the conventional theory is found within the present experimental accuracy.Partially supported by the Deutsche Forschungsgemeinschaft (SFB 201)