Two-body Photodisintegration Research Articles

First measurement of the asymmetry and the Gerasimov-Drell-Hearn integrand from the He3⃗(γ⃗,p)H2 reaction at an incident photon energy of 29 MeV

The first measurement of the $\vec{^3He}(\vec{\gamma},p)d$ process was performed at the High Intensity $\gamma$-ray Source (HI$\gamma$S) facility at Triangle Universities Nuclear Laboratory (TUNL) using a circularly polarized, monoenergetic $\gamma$-ray beam and a longitudinally polarized $^3$He target. The spin-dependent asymmetry and the contribution from the two-body photodisintegration to the $^3$He Gerasimov-Drell-Hearn integrand are extracted and compared with state-of-the-art three-nucleon system calculations at the incident photon energy of 29.0 MeV. The data are in general agreement with the various theoretical predictions based on the Siegert theorem or on explicit inclusion of meson-exchange currents.

Photodisintegration of Light Nuclei

Recent results of photodisintegration of deuteron and 3He measured with the CEBAF Large Acceptance Spectrometer at Jefferson Lab are reported. The onset of dimensional scaling is investigated in the two-body photodisintegration of 3He, with the results indicating a scaling onset at remarkably low energy and momentum transfer. Results on the azimuthal asymmetry of deuteron photodisintegration are expected to aid in understanding the dominant mechanisms of deuteron photodisintegration and the underlying dynamics in the medium-energy region. In this region, neither effective field theories nor perturbative QCD can be used to describe the reaction, and understanding the underlying dynamics is based on phenomenological quark models.

Recent Results from CLAS on Baryon Structure and Interactions

The understanding of baryon structure and interactions from Quantum Chromodynamics is one of the main objectives of modern hadron physics. Of particular interest is the regime of confinement where perturbative methods are not applicable to derive testable predictions. Understanding the transition from hadronic to partonic degrees of freedom, the hyperon-nucleon interaction, and nuclei in terms of quarks and gluons are some of the key problems. Here we present results of photoproduction experiments on light nuclear targets from Jefferson Lab Hall B. Our observation of onset of dimensional scaling in the cross section of two-body photodisintegration of 3He at energy and momentum transfer well below 1 GeV suggests that quarks and gluons may be relevant degrees of freedom for the description of nuclear dynamics at energies lower than previously considered. Our program to study lambda-nucleon scattering via a large set of polarization observables for final-state interactions in exclusive hyperon photoproduction off the deuteron has produced preliminary results for single-polarization observables. The beam-spin asymmetry shows interesting features at large lambda polar angles and large kaon momenta.

Photodisintegration Cross Section of the ReactionHe4(γ,p)H3between 22 and 30 MeV

The two-body photodisintegration cross section of (4)He into a proton and triton was measured with monoenergetic photon beams in 0.5 MeV energy steps between 22 and 30 MeV. High-pressure (4)He-Xe gas scintillators of various (4)He/Xe ratios served as targets and detectors. Pure Xe gas scintillators were used for background studies. A NaI detector together with a plastic scintillator paddle was employed for determining the incident photon flux. Our comprehensive data set follows the trend of the theoretical calculations of the Trento group very well, although our data are consistently lower in magnitude by about 5%. However, they differ significantly from the majority of the previous data, especially from the recent data of Shima et al. The latter data had put into question the validity of theoretical approaches used to calculate core-collapse supernova explosions and big-bang nucleosynthesis abundances of certain light nuclei.

Two-body photodisintegration of 3He between 7 and 16 MeV

A comprehensive data set is reported for the two-body photodisintegration cross section of 3He using mono-energetic photon beams at eleven energies between 7.0 and 16.0 MeV. A He3+Xe high-pressure gas scintillator served as target and detector. Although our data are in much better agreement with our state-of-the-art theoretical calculations than the majority of the previous data, these calculations underpredict the new data by about 10%. This disagreement suggests an incomplete understanding of the dynamics of the three-nucleon system and its response to electromagnetic probes.

Two-body photodisintegration of 3He between 7 and 16 MeV

Two-body photodisintegration of 3He between 7 and 16 MeV

Triton Photodisintegration with Effective Field Theory

Effective field theory (EFT) has been recently used for the calculation of neutron-deuteron radiative capture at very low energies.We present here the use of EFT to calculate the two-body photodisintegration of the triton, considering the three-body force. The calculated cross section shows sharp rising from threshold to maximum about 0.88 mb at 13 MeV and decreasing slightly to about 0.81 mb at 19 MeV, in agreement with the experimental data. Our results are in good agreement with the experimental data and the other calculations using modern realistic two- and three-nucleon forces, like AV18/UrbanaIX potential.

Measurement of the differential cross section for the two-body photodisintegration ofHe3atθLAB=90°using tagged photons in the energy range14−31MeV

The two-body photodisintegration of He-3 has been investigated using tagged photons with energies from 14-31 MeV at MAX-lab in Lund, Sweden. The two-body breakup channel was unambiguously identified by the (nonsimultaneous) detection of both protons and deuterons. This approach was made feasible by the overdetermined kinematic situation afforded by the tagged-photon technique. Proton-and deuteron-energy spectra were measured using four silicon surface-barrier detector telescopes located at a laboratory angle of 90 degrees with respect to the incident photon-beam direction. Average statistical and systematic uncertainties of 5.7% and 6.6% in the differential cross section were obtained for 11 photon-energy bins with an average width of 1.2 MeV. The results are compared to previous experimental data measured at comparable photon energies as well as to the results of two recent Faddeev calculations which employ realistic potential models and take into account three-nucleon forces and final-state interactions. Both the accuracy and precision of the present data are improved over those obtained in the previous measurements. The data are in good agreement with most of the previous results, and favor the inclusion of three-nucleon forces in the calculations. (Less)

Photodisintegration ofHe4intop+t

The two-body photodisintegration of $^4$He into a proton and a triton has been studied using the CEBAF Large-Acceptance Spectrometer (CLAS) at Jefferson Laboratory. Real photons produced with the Hall-B bremsstrahlung-tagging system in the energy range from 0.35 to 1.55 GeV were incident on a liquid $^4$He target. This is the first measurement of the photodisintegration of $^4$He above 0.4 GeV. The differential cross sections for the $\gamma$$^4$He$\to pt$ reaction have been measured as a function of photon-beam energy and proton-scattering angle, and are compared with the latest model calculations by J.-M. Laget. At 0.6-1.2 GeV, our data are in good agreement only with the calculations that include three-body mechanisms, thus confirming their importance. These results reinforce the conclusion of our previous study of the three-body breakup of $^3$He that demonstrated the great importance of three-body mechanisms in the energy region 0.5-0.8 GeV .

Two-body photodisintegration of 3He, 4He, and 2He up to 1.5 GeV

Preliminary Jefferson Lab data on the photodisintegration of the isotopes of helium are presented and discussed.

Recoil-Proton Polarization in High-Energy Deuteron Photodisintegration with Circularly Polarized Photons

We measured the angular dependence of the three recoil-proton polarization components in two-body photodisintegration of the deuteron at a photon energy of 2 GeV. These new data provide a benchmark for calculations based on quantum chromodynamics. Two of the five existing models have made predictions of polarization observables. Both explain the longitudinal polarization transfer satisfactorily. Transverse polarizations are not well described, but suggest isovector dominance.

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).

Polarization observables in high-energy deuteron photo-disintegration within the Quark-Gluon Strings Model

Deuteron two-body photodisintegration is analysed within the framework of the Quark-Gluon Strings Model. The model describes fairly well the recent experimental data from TJNAF in the few GeV region. Angular distributions at different $\gamma$ -energies are presented and the effect of a forward-backward asymmetry is discussed. New results from the QGSM for polarization observables from 1.5-6 GeV are presented and compared with the available data.

Forward-backward angle asymmetry and polarization observables in high-energy deuteron photodisintegration

Deuteron two-body photodisintegration is analysed within the framework of the Quark-Gluon Strings Model. It is found that the forward-backward angle asymmetry predicted by the model is confirmed by the recent data at different photon energies from Jlab. New calculations for polarization observables, the cross section asymmetry $\Sigma$ and the polarization transfer $C_{z^{\prime}}$, for photon energies $(1.2\div6)$ GeV are presented and compared with the data available up to 2 GeV.

Deuteron photodisintegration in the quark-hadron picture

The study of the two-body photodisintegration of the deuteron in the few GeV region is the ideal reaction to clarify the transition from the nucleonic degrees of freedom to the QCD picture of hadrons. The CLAS large angle spectrometer of Hall B at Jlab allowed for the first time the complete measurement of the angular distribution of the differential cross section at photon energy between 0.5 and 3 GeV. Preliminary results of the E93-017 experiment from the analysis of the 30% of the total statistic accumulated show persistent forward-backward asymmetry and are well described by the recent calculation of the deuteron photodisintegration cross section derived in the framework of the Quark Gluon String Model.

Trinucleon Photo-Reactions with Δ-Isobar Excitation: Radiative Nucleon-Deuteron Capture and Two-Body Photo-Disintegration of the Three-Nucleon Bound State

Radiative nucleon-deuteron capture and photo disintegration of the three-nucleo n bound state with two-body final states are described. The description uses nucleon degrees of freedom extended to include the excitation of a single nucleon to a \diso. The baryonic interaction and the electromagnetic cu rrent couple nucleonic states and states with a \diso. Exact solutions of three-p article scattering equations are employed for the initial or final states of the reactions. The current has one-baryon and two-baryon contributions. The role of t he \diso in the description of the considered photo reactions is discussed and fo und to be moderate. The spin observables $A_{yy}$ and $T_{20}$ at $90^{\circ}$ la b scattering angle can be calculated model-independently from the $E1$ Siegert te rm in the long-wavelength limit.

Deuteron photodisintegration within the Quark-Gluon Strings Model and QCD motivated nonlinear Regge trajectories

We investigate deuteron two-body photodisintegration within the framework of the Quark-Gluon Strings Model with nonlinear baryon Regge trajectories. Special attention is paid to the use of QCD motivated Regge trajectories of the logarithmic and square-root form which have been suggested recently by Brisudov\'{a}, Burakovsky and Goldman. We find that the recent experimental data from TJNAF in the few GeV region can reasonably be described by the model. Angular distributions at different $\gamma$-energies are presented and the effect of a forward-backward asymmetry is discussed. Predictions for the energy dependence of $d\sigma/dt$ at higher energies and different $\Theta_{cm}$ are presented, too.

Dynamical Study of $^1\hbox {H}(\vec {d},{\gamma})^3\hbox {He}$ Tensor Observables in the Energy Range of 80 keV to 95 MeV: Tests of Effective Two-Body Models

Realistic interactions are used to study \(\) tensor observables in the energy range of 80 keV to 95 MeV deuteron laboratory energy, as well as the differential cross section for the two-body photodisintegration of \(\). The Siegert form of the E1 multipole operator in the long-wavelength limit is taken as the sole component of the electromagnetic interaction. The three-body Faddeev equations for the bound-state and continuum wave functions are solved using the Paris, Argonne V14, Bonn-A, and Bonn-B potentials. The corresponding nucleon-nucleon t-matrices are represented in a separable form using the Ernst-Shakin-Thaler representation. The Coulomb force between protons is neglected and no three-nucleon force is included. The contribution of nucleon-nucleon P-wave components to the observables is carefully studied, not only in the angular distribution of the observables, but also as a function of the deuteron laboratory energy for fixed centre-of-mass angle. Comparison with data is shown wherever it exists.

QCD Rescattering and High Energy Two-Body Photodisintegration of the Deuteron

Photon absorption by a quark in one nucleon followed by its high-momentum transfer interaction with a quark in the other may produce two final-state nucleons with high relative momentum. We sum the relevant quark rescattering diagrams to show that the scattering amplitude depends on a convolution between the large angle pn scattering amplitude, the hard photon-quark interaction vertex, and the low-momentum deuteron wave function. The computed absolute values of the cross section are in reasonable agreement with the data.

QCD rescattering and high energy two-body photodisintegration of the deuteron

Photon absorption by a quark in one nucleon followed by its high momentum transfer interaction with a quark in the other may produce two nucleons with high relative momentum. We sum the relevant quark rescattering diagrams, to show that the scattering amplitude depends on a convolution between the large angle $pn$ scattering amplitude, the hard photon-quark interaction vertex and the low-momentum deuteron wave function. The computed cross sections are in reasonable agreement with the data.