Two-body Deuteron Photodisintegration Research Articles

Photoreactions with tensor-polarized deuterium target at VEPP–3

We give an overview of the activity in studying photoprocesses on a tensor-polarized deuterium target, which is carried out at the VEPP–3 electron storage ring. Recent experimental results on tensor asymmetries in two-body deuteron photodisintegration at the photon energy up to 500 MeV, and in coherent pion photoproduction on deuteron are presented. Plans to upgrade the facility and future experiments are discussed. Further progress is connected with the installation of a tagging system for almost-real photons. This would allow us to extend the measurements of polarization observables in photonuclear reactions on deuteron up to a photon energy of 1.5 GeV and permit to perform double polarized experiments – with linear polarized photon beams and tensor/vector polarized deuterium targets.

Nucleon-nucleon wave function with short-range nodes and high-energy deuteron photodisintegration

We review a concept of the Moscow potential of the $\mathit{NN}$ interaction. On the basis of this concept, we derive by quantum inversion optical partial potentials from the modern partial-wave analysis data and deuteron properties. Point-form relativistic quantum mechanics is applied to the two-body deuteron photodisintegration. Calculations of the cross-section angular distributions cover photon energies between 1.1 and 2.5 GeV. Good agreement between our theory and recent experimental data confirms the concept of deep attractive Moscow potential with forbidden $S$ and $P$ states.

Measurement and simulation of the neutron response of the Nordball liquid scintillator array

The response of the liquid scintillator array Nordball to neutrons in the energy range 1.5 < T n < 10 MeV has been measured by time of flight using a 252Cf fission source. Fission fragments were detected by means of a thin-film plastic scintillator. The measured differential and integral neutron detection efficiencies agree well with predictions of a Monte Carlo simulation of the detector which models geometry accurately and incorporates the measured, non-linear proton light output as a function of energy. The ability of the model to provide systematic corrections to photoneutron cross-sections, measured by Nordball at low energy, is tested in a measurement of the two-body deuteron photodisintegration cross-section in the range E γ = 14 – 18 MeV . After correction the present H 2 ( γ , n ) p measurements agree well with a published evaluation of the large body of H 2 ( γ , p ) n data.

Complete angular distribution measurements of two-body deuteron photodisintegration between 0.5 and 3GeV

Nearly complete angular distributions of the two-body deuteron photodisintegration differential cross section have been measured using the CLAS detector and the tagged photon beam at JLab. The data cover photon energies between 0.5 and 3.0 GeV and center-of-mass proton scattering angles 10-160 degrees. The data show a persistent forward-backward angle asymmetry over the explored energy range, and are well-described by the non-perturbative Quark Gluon String Model.

Deuteron photodisintegration at high energy

The high-energy two-body deuteron break-up is a very well-suited process to identify quark effects in nuclei. In particular, its study in the few GeV region can clarify the transition from the nucleonic to the QCD picture of hadrons. The CEBAF Large Angle Spectrometer (CLAS) at JLab allowed for the first time the complete measurement of the angular distributions of the two-body deuteron photodisintegration differential cross-section at photon energies from 0.5 to 2.95 GeV. First results from the analysis of 30% of the total collected data show persistent forward-backward asymmetry and are well described by a calculation derived in the non-perturbative framework of the Quark Gluon String Model (QGSM).

High energy angular distribution measurements of the exclusive deuteron photodisintegration reaction

The first complete measurements of the angular distributions of the two-body deuteron photodisintegration differential cross section at photon energies above 1.6 GeV were performed at the Thomas Jefferson National Accelerator Facility. The results show a persistent forward-backward asymmetry up to E_γ=2.4GeV, the highest-energy measured in this experiment. The Hard Rescattering and the Quark-Gluon string models are in fair agreement with the results.

Effects of negative-energy components in two-body deuteron photodisintegration

Several observables in two-body deuteron photodisintegration are investigated in the framework of the Bethe-Salpeter formalism. Apart from keeping the Lorentz covariance throughout, special attention is paid to inclusion of both the positive-energy and negative-energy partial-wave components of the deuteron state. Using the Bethe-Salpeter equation for the deuteron in the ladder approximation with one-boson exchanges as a driving term, the contribution of the negative-energy states is studied for the unpolarized differential cross section as well as for linear photon and tensor target asymmetries. These states are found to have an impact on the observables and, thus, should be taken into account in a complete theoretical treatment of the reaction in the intermediate energy regime.

Measurement of the high energy two-body deuteron photodisintegration differential cross section.

The first measurements of the d(gamma,p)n differential cross section at forward angles and photon energies above 4 GeV were performed at the Thomas Jefferson National Accelerator Facility (JLab). The results indicate evidence of an angular dependent scaling threshold. Results at straight theta(cm) = 37 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 4 GeV, while those at 70 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 1.5 GeV.

High energy deuteron photodisintegration

Results are presented for two-body deuteron photodisintegration, i.e. d(γ,p)n, at θ CM = 90° and for photon energies up to 1.6 GeV. These results are discussed in the light of several theoretical models. The data suggest that, at the highest energies, the energy dependence of the cross section is that given by simple constituent counting. We also discuss the need for additional work, both experimental and theoretical, to help resolve conflicting points of view.

Measurement of the differential cross section for the reaction 2H( gamma,p)n at high photon energies and theta c.m.

We have measured the differential cross section for two-body deuteron photodisintegration at θc.m.=90° and for photon energies between 0.8 and 1.6 GeV. At energies above ≃ 1.2 GeV, the data appear to obey a simple scaling law predicted by constituent-counting rules assuming parton degrees of freedom for the deuteron and nucleons. Agreement with model calculations based on meson exchange or reduced nuclear amplitudes is discussed.

Two-body deuteron photodisintegration above pion threshold with a dynamical treatment of δ degrees of freedom

The two-body photo break-up of the deuteron above pion threshold is calculated treating the final state interaction in a coupled channel approach with inclusion of Δ degrees of freedom. For the electromagnetic interaction nucleon, isobar and meson exchange currents are taken into account. Various observables (total and differential cross sections, γ-asymmetry and nucleon polarization) are influenced by the dynamical treatment of Δ degrees of freedom. Especially for the proton polarization it leads to an improved agreement with experiment. However, the situation for the shape of the differential cross section remains problematic.