arXiv subjects

J. Golak

Publications and source records attributed to J. Golak.

At least 127 records · Page 7Linked to original sources

arXiv2003

Three-Nucleon Photodisintegration of 3He

The three-nucleon photodisintegration of 3He has been calculated in the whole phase space using consistent Faddeev equations for the three-nucleon bound and scattering states. Modern nucleon-nucleon and 3N forces have been applied as well as different approaches to nuclear currents. Phase space regions are localized where 3N force effects are especially large. In addition semi-exclusive cross sections for 3He(gamma,N) have been predicted which carry interesting peak structures. Finally some data for the exclusive 3N breakup process of 3He and its total breakup cross section have been compared to theory.

nucl-th↗

arXiv2003

Search for Three-Nucleon Force Effects in Two-Body Photodisintegration of 3He(3H) and in the Time Reversed Proton-Deuteron Radiative Capture Process

Faddeev calculations have been performed for nucleon-deuteron photodisintegration of 3He(3H) and proton-deuteron radiative capture. The bulk of the results is based on the AV18 nucleon-nucleon force and the Urbana IX three-nucleon force together with explicit exchange currents or applying the Siegert approach. Three-nucleon force effects are predicted for both processes and supported by most of the data.

nucl-th↗

arXiv2003

Final State Interaction Effects in pol 3He(pol e,e'p)

Asymmetries in quasi-elastic pol 3He(pol e,e'p) have been measured at a momentum transfer of 0.67 (GeV/c)^2 and are compared to a calculation which takes into account relativistic kinematics in the final state and a relativistic one-body current operator. With an exact solution of the Faddeev equation for the 3He-ground state and an approximate treatment of final state interactions in the continuum good agreement is found with the experimental data.

nucl-ex↗

arXiv2003

Effects of the magnetic moment interaction between nucleons on observables in the 3N continuum

The influence of the magnetic moment interaction of nucleons on nucleon-deuteron elastic scattering and breakup cross sections and on elastic scattering polarization observables has been studied. Among the numerous elastic scattering observables only the vector analyzing powers were found to show a significant effect, and of opposite sign for the proton-deuteron and neutron-deuteron systems. This finding results in an even larger discrepancy than the one previously established between neutron-deuteron data and theoretical calculations. For the breakup reaction the largest effect was found for the final-state-interaction cross sections. The consequences of this observation on previous determinations of the ^1S_0 scattering lengths from breakup data are discussed.

nucl-th↗

arXiv2002

Lorentz Boosted NN Potential for Few-Body Systems: Application to the three-nucleon bound state

A Lorentz boosted two-nucleon potential is introduced in the context of equal time relativistic quantum mechanics. The dynamical input for the boosted nucleon-nucleon (NN) potential is based on realistic NN potentials, which by a suitable scaling of the momenta are transformed into NN potentials belonging to a relativistic two-nucleon Schroedinger equation in the c.m. system. This resulting Lorentz boosted potential is consistent with a previously introduced boosted two-body t-matrix. It is applied in relativistic Faddeev equations for the three-nucleon bound state to calculate the ^3H binding energy. Like in previous calculations the boost effects for the two-body subsystems are repulsive and lower the binding energy.

nucl-th↗

arXiv2002

Theoretical predictions for extraction of GEn from semi-inclusive electron scattering on polarized 3He based on various nucleon-nucleon interactions

The process 3He(e,e'n) with polarized electrons and 3He in the initial state is theoretically analyzed with the aim to search for sensitivity to the electric form factor of the neutron, GEn. Faddeev calculations based on five high precision nucleon-nucleon force models are employed and stability versus exchange of the nucleon-nucleon forces is demonstrated.

nucl-th↗

arXiv2002

Three-Nucleon Force Effects in Nucleon Induced Deuteron Breakup: Predictions of Current Models (I)

An extensive study of three-nucleon force effects in the entire phase space of the nucleon-deuteron breakup process, for energies from above the deuteron breakup threshold up to 200 MeV, has been performed. 3N Faddeev equations have been solved rigorously using the modern high precision nucleon-nucleon potentials AV18, CD Bonn, Nijm I, II and Nijm 93, and also adding 3N forces. We compare predictions for cross sections and various polarization observables when NN forces are used alone or when the two pion-exchange Tucson-Melbourne 3NF was combined with each of them. In addition AV18 was combined with the Urbana IX 3NF and CD Bonn with the TM' 3NF, which is a modified version of the TM 3NF, more consistent with chiral symmetry. Large but generally model dependent 3NF effects have been found in certain breakup configurations, especially at the higher energies, both for cross sections and spin observables. These results demonstrate the usefulness of the kinematically complete breakup reaction in testing the proper structure of 3N forces.

nucl-th↗

arXiv2002

Three-Nucleon Force Effects in Nucleon Induced Deuteron Breakup: Comparison to Data (II)

Selected Nd breakup data over a wide energy range are compared to solutions of Faddeev equations based on modern high precision NN interactions alone and adding current three-nucleon force models. Unfortunately currently available data probe phase space regions for the final three nucleon momenta which are rather insensitive to 3NF effects as predicted by current models. Overall there is good to fair agreement between present day theory and experiment but also some cases exist with striking discrepancies. Regions in the phase space are suggested where large 3NF effects can be expected.

nucl-th↗

arXiv2002

The $^3$He(e, e$'$d)p Reaction in q$ω$-constant Kinematics

The cross section for the $^3$He(e, e$'$d)p reaction has been measured as a function of the missing momentum $p_m$ in q$ω$ -constant kinematics at beam energies of 370 and 576 MeV for values of the three-momentum transfer $q$ of 412, 504 and 604 \mevc. The L(+TT), T and LT structure functions have been separated for $q$ = 412 and 504 \mevc. The data are compared to three-body Faddeev calculations, including meson-exchange currents (MEC), and to calculations based on a covariant diagrammatic expansion. The influence of final-state interactions and meson-exchange currents is discussed. The $p_m$-dependence of the data is reasonably well described by all calculations. However, the most advanced Faddeev calculations, which employ the AV18 nucleon-nucleon interaction and include MEC, overestimate the measured cross sections, especially the longitudinal part, and at the larger values of $q$. The diagrammatic approach gives a fair description of the cross section, but under(over)estimates the longitudinal (transverse) structure function.

nucl-ex↗

arXiv2002

Spin dependent momentum distributions of proton-deuteron clusters in 3He from electron scattering on polarized 3He: theoretical predictions

The process $\overrightarrow{^3{\rm He}}(e,e'\vec{p})d $ (or $\overrightarrow{^3{\rm He}}(e,e'\vec{d})p $) is studied theoretically in a Faddeev treatment with the aim to have access to the spin-dependent momentum distribution of ${\vec p} {\vec d} $ clusters in polarized $^3$He. Final state interactions and meson exchange currents turn out to have a strong influence in the considered kinematical regime (below the pion threshold). This precludes the direct access to the momentum distribution except for small deuteron momenta. Nevertheless, the results for the longitudinal and transverse response functions are interesting as they reflect our present day understanding of the reaction mechanism and therefore data would be very useful.

nucl-th↗

arXiv2002

Benchmark Calculation of the Three-Nucleon Photodisintegration

A benchmark is set on the three-nucleon photodisintegration calculating the total cross section with modern realistic two- and three-nucleon forces (AV18, UrbIX) using both the Faddeev equations and the Lorentz Integral Transform method. This test shows that the precision of three-body calculations involving continuum states is considerably higher than experimental uncertainties. Effects due to retardations, higher multipoles, meson exchange currents and Coulomb force are studied.

nucl-th↗

arXiv2001

Sensitivity Studies for Extraction of G_E^n from Inclusive and Semi-inclusive Electron Scattering on Polarized 3He

The processes \vec{3He}(\vec{e},e') and \vec{3He}(\vec{e},e'n) are theoretically analyzed with the aim to search for sensitivities in the electric form factor of the neutron, G_E^n. Faddeev calculations based on the high precision NN force AV18 and using consistent MEC's are employed. While the inclusive process is too insensitive, the semi-exclusive one appears promising.

nucl-th↗

arXiv2001

Few-Nucleon Calculations and Correlations

Some present day results for few-nucleon bound state, two-nucleon correlation functions and scattering observables are briefly reviewed. The old idea of the Coulomb sum rule as a way to extract the pp correlation function is reconsidered. It appears to be an ideal case to probe properties of the density operator and the ground state wave functions without disturbances of final state interactions (FSI) in exclusive electron scattering on 3He. Also exclusive photodisintegration of 3He is regarded which appears to be promising to identify 3N force effects.

nucl-th↗

arXiv2000

Nucleon-deuteron elastic scattering as a tool to probe properties of three-nucleon forces

Faddeev equations for elastic Nd scattering have been solved using modern NN forces combined with the Tucson-Melbourne two-pion exchange three-nucleon force, with a modification thereof closer to chiral symmetry and the Urbana IX three-nucleon force. Theoretical predictions for the differential cross section and several spin observables using NN forces only and NN forces combined with three-nucleon force models are compared to each other and to the existing data. A wide range of energies from 3 to 200 MeV is covered. Especially at the higher energies striking three-nucleon force effects are found, some of which are supported by the still rare set of data, some are in conflict with data and thus very likely point to defects in those three-nucleon force models.

nucl-th↗

arXiv2000

Investigation of the Exclusive 3He(e,e'pp)n Reaction

Cross sections for the 3He(e,e'pp)n reaction were measured over a wide range of energy and three- momentum transfer. At a momentum transfer q=375 MeV/c, data were taken at transferred energies omega ranging from 170 to 290 MeV. At omega=220 MeV, measurements were performed at three q values (305, 375, and 445 MeV/c). The results are presented as a function of the neutron momentum in the final-state, as a function of the energy and momentum transfer, and as a function of the relative momentum of the two-proton system. The data at neutron momenta below 100 MeV/c, obtained for two values of the momentum transfer at omega=220 MeV, are well described by the results of continuum-Faddeev calculations. These calculations indicate that the cross section in this domain is dominated by direct two-proton emission induced by a one-body hadronic current. Cross section distributions determined as a function of the relative momentum of the two protons are fairly well reproduced by continuum-Faddeev calculations based on various realistic nucleon-nucleon potential models. At higher neutron momentum and at higher energy transfer, deviations between data and calculations are observed that may be due to contributions of isobar currents.

nucl-ex↗

arXiv2000

Extraction of electromagnetic neutron form factors through inclusive and exclusive polarized electron scattering on polarized 3He target

Inclusive 3He(e,e') and exclusive 3He(e,e'n) processes with polarized electrons and 3He have been theoretically analyzed and values for the magnetic and electric neutron form factors have been extracted. In both cases the form factor values agree well with the ones extracted from processes on the deuteron. Our results are based on Faddeev solutions, modern NN forces and partially on the incorporation of mesonic exchange currents.

nucl-th↗

arXiv2000

Faddeev Calculations of Proton-Deuteron Radiative Capture with Exchange Currents

pd capture processes at various energies have been analyzed based on solutions of 3N-Faddeev equations and using modern NN forces. The application of the Siegert theorem is compared to the explicit use of $π$- and $ρ$-like exchange currents connected to the AV18 NN interaction. Overall good agreement with cross sections and spin observables has been obtained but leaving room for improvement in some cases. Feasibility studies for 3NF's consistently included in the 3N continuum and the 3N bound state have been performed as well.

nucl-th↗

arXiv1999

Investigation of the Exclusive 3He(e,e'pp) Reaction

Cross sections for the 3He(e,e'pp)n reaction were measured at an energy transfer of 220 MeV and three-momentum transfers q of 305, 375, and 445 MeV/c. Results are presented as a function of q and the final-state neutron momentum for slices in specific kinematic variables. At low neutron momenta, comparison of the data to results of continuum Faddeev calculations performed with the Bonn-B nucleon-nucleon potential indicates a dominant role for two-proton knockout induced by a one-body hadronic current.

nucl-ex↗