Realistic NN Potentials Research Articles

Longitudinal electron scattering response functions ofH3andHe3

Trinucleon longitudinal response functions R_L(q,omega) are calculated for q values up to 500 MeV/c. These are the first calculations beyond the threshold region in which both three-nucleon (3N) and Coulomb forces are fully included. We employ two realistic NN potentials (configuration space BonnA, AV18) and two 3N potentials (UrbanaIX, Tucson-Melbourne). Complete final state interactions are taken into account via the Lorentz integral transform technique. We study relativistic corrections arising from first order corrections to the nuclear charge operator. In addition the reference frame dependence due to our non-relativistic framework is investigated. For q less equal 350 MeV/c we find a 3N force effect between 5 and 15 %, while the dependence on other theoretical ingredients is small. At q greater equal 400 MeV/c relativistic corrections to the charge operator and effects of frame dependence, especially for large omega, become more important. In comparison with experimental data there is generally a rather good agreement. Exceptions are the responses at excitation energies close to threshold, where there exists a large discrepancy with experiment at higher q. Concerning the effect of 3N forces there are a few cases, in particular for the R_L of 3He, where one finds a much improved agreement with experiment if 3N forces are included.

Do we understand the $\eta N$ interaction from the near-threshold $\eta$ photoproduction on the deuteron?

The effects of final-state interaction in incoherent $\eta$ photoproduction on a deuteron are studied within a three-body approach including a realistic NN potential. The results are compared with available data, and differences with other theoretical predictions are analyzed. The role of the $\eta N$ interaction and the possibility of extracting the $\eta N$ scattering parameters from this reaction are discussed.

Nucleon–nucleon scattering in a three-dimensional approach

The nucleon-nucleon t-matrix is calculated directly as function of two vector momenta for different realistic NN potentials. The angular and momentum dependence of the full amplitude is studied and NN observables are calculated.

Probing short-range nucleon-nucleon correlations with virtual photons at MAMI

Nucleon-nucleon correlations were studied in two ( e, e′ pp) experiments. The first one, on 12 C, was performed in close to 4π geometry at E beam = 705 MeV, ω = 225 MeV, and q = 412 MeV/c. The electrons were observed in a large-acceptance magnetic spectrometer in coincidence with protons detected in a BGO crystal ball. Missing energy and momentum, relative momentum and angular distributions were derived and compared with a facorised two-nucleon emision model. A G-matrix correlation function is favoured by the data. The second experiment was a high resolution study of the reaction 16 O( e, e′ pp) 14 C in super-parallel kinematics. Three magnetic spectrometers were used in coincidence at E beam = 855 MeV, ω = 215 MeV, q = 316 MeV/c. A missing momentum (pair momentum) range −100 MeV/c ≤ P m ≤ 450 MeV/c was sampled. Two-hole states were preferentially excited, with an energy resolution of 500 keV. Their momentum distributions are compared with unfactorised model calculations which make use of realistic NN potentials.

The complex Kohn variational method applied to N-d scattering

The three-nucleon ground state and the N-d scattering states are obtained using variational principles. The wave function of the system is decomposed into angular-spin-isospin channels and the corresponding two dimensional spatial amplitudes are expanded in a correlated polynomial basis. For the scattering states, the complex form of the Kohn variational principle is used to determine the S-matrix. Special attention is given to the convergence pattern of the phase-shift and mixing parameters. The calculations have been performed using realistic local NN potentials and three-nucleon forces. Important features of the method are anomaly-free solutions and the low dimensionality of the matrices involved allowing for the inclusion of a large number of states. Very precise and stable numerical results have been obtained.

Measurement of polarization transfer and the tensor analyzing power in polarized deuteron break-up with deuteron momenta up to 9 GeV/ c

New experimental results for polarization transfer, κ 0 and the analyzing power, T 20, in 12 C( d , p) X at 0° are present. The measurements have been performed at the Dubna polarized deuteron facility. At high intrinsic momenta of the proton in the deuteron ( k⩾300 MeV/ c) the behaviour of these observables is in disagreement with the impulse approximation predictions based on realistic NN-potentials. The data are compared with calculations of some other models predicting the high k behaviour of κ 0 and T 20.

On the occurrence of cooper-like pairs in infinite nuclear matter

The possible occurrence of Cooper-like pairs in infinite nuclear matter is examined in the frame of Bruckner theory with a realisticN-N potential (RSC). It is found that they arise both in the3S1 and in the1S0 channel, the former being always favoured. Moreover a phase transition is found at low density, from a nuclear bound state to an assembly of deuterons.

Study of the kinematically complete breakup reaction 2H(p̄, pp)n at Ep = 3 Mev with polarized protons

The breakup reaction 2H(p̄, pp)n at E p = 13.0 MeV has been measured in a kinematically complete experiment with polarized protons in four special kinematical situations: np final-state interaction, pp quasi-free scattering, collinearity and symmetric space star. These configurations are identical to those of a corresponding 2H(n, nn) 1H experiment. The cross sections d 3σ/ dΩ 3 dΩ 4 dS and the vector analyzing powers A 1 are presented as a function of the arclenght of the relevant kinematical loci. They are compared to the rigorous Faddeev calculations using realistic meson-exchange NN potentials, i.e. the Paris and Bonn potential. Comparison with the cross section data of the analog neutron experiment is made. In the quasi-free scattering and the space-star cross sections marked discrepancies with the theoretical predictions, in the latter case also with the neutron results are found. In the collinear and final-state interaction situations the agreement is rather good as well as for all analyzing powers and is even improved by taking the finite angular spread into account.

Proton and triton momentum distributions from4He fragmentation at relativistic energies

The 0° differential cross sections of the12C(4He,p) and12C(4He,t) reactions have been measured at beam momenta of 4.52 and 2.69 GeV/c/nucleon, respectively. The proton and triton momentum distributions in4He are extracted from the cross sections using a relativistic impulse approximation. Some theoretical models based on realisticN-N potentials are examined for our data.

Bonn potential and electron-deuteron scattering at high momentum transfer.

Deuteron electrodisintegration d(e,e') near threshold is calculated using the various energy-independent Bonn potential versions. At high momentum transfer they lead to rather different results compared to other realistic NN potentials. This can only be partly explained by a different D-state admixture strength. The potential effect is particularly strong for the transverse form factor, but is also present for the longitudinal one. The latter is influenced in a similar way as the longitudinal part of the elastic deuteron form factor A(${\mathit{q}}^{2}$) which we have considered in addition.

Test of forbidden state NN potential in the 3N system.

Significant underbinding for the triton of a quantum-chromodynamically motivated realistic NN potential containing a superdeep short-ranged attraction and a forbidden state in the S-italic waves has been reported from a previous Faddeev calculation. In the present paper, this feature is reproduced with a simple S-italic-wave-interaction model of this NN potential, generalized into a wide range in the form of a short distance node, and explained in terms of short-ranged NN D-italic-wave components which the nodal S-italic-wave components introduce inevitably through the three-body kinematics. The strengths of the NN D-italic-wave interactions are estimated to be not sufficient to compensate for the kinetic energies arising from these D-italic-wave components, which means a significant loss for 3N binding. This is in sharp contrast to the strong 3..cap alpha.. binding in the forbidden state ..cap alpha cap alpha.. potential model which is supported by strong D-italic- and G-italic-wave interactions. The present study indicates that a noticeable short distance node in the 2N wave function is unlikely.

Coulomb corrections to alpha - alpha phase shifts.

Realistic NN potentials like the Paris and the Bonn potential give different results for peripheral ..cap alpha..-..cap alpha.. phase shifts at low energy, with resulting consequences for the polarization of ..cap alpha.. particles. To study the hadronic ..cap alpha..-..cap alpha.. interaction in more detail, we have considered the Coulomb corrections to the phase shifts and compared them with model-independent predictions.

Relativistic correction to the deuteron magnetic moment and angular condition

The relativistic correction (RC) to the deuteron magnetic moment is calculated using the light-cone dynamics. The restrictions imposed by the angular condition on the electromagnetic current operator of the deuteron are discussed in detail. It is shown that the additive model for the current operator of interacting constituents is consistent with the angular condition only for the two first terms of the expansion of the “good” current component j + = 1 2 (j 0 + j z ) in powers of the momentum transfer q. The RC to μ d is expressed through the matrix element of the “good” component j + and is found to be equal to (0.6–0.8) × 10 −2 e h ̵ /2m p c for realistic NN potentials. Taking account of RC decreases essentially the discrepancy between the theoretical and experimental values of μ d. Possible solutions of the angular condition for squared q-terms of the j + current component are also discussed.

Mass-difference effects in the NN system

It is shown that the mass-difference effects of the difference between the pp and nn scattering lengths can become anomalously large by off-shell effects. The author's result shows clearly how this mass-difference correction depends on the off-shell behaviour of an interaction model. A comparison of theoretical results and experimental data gives a constraint on the half-shell function at the threshold. Charge-symmetry-breaking effects play an important role in the description of the data by realistic NN potentials such as the Paris potential.

The NN-potential with forbidden state suggested from a six-quark model with one-pion exchange

A new, realistic NN-potential is proposed which is suggested from a six-quark model with dominant quark configuration s 4p 2 and includes the one-pion exchange mechanism in the 1S 0 and coupled 3S 1 − 3D 1 channels. The potential is purely attractive on the mass shell and includes a deep-lying forbidden state instead of a repulsive core. A very small number of free parameters is sufficient to succesfully describe both the 3S 1 − 3D 1 NN-phase shifts, the mixing parameter ε and the singlet 1S 0 phase shifts in a broad energy range from 0 to 400 MeV (alongside with effective range parameters) and also basic deuteron parameters (i.e. binding energy, RMS charge radius, quadrupole moment, etc.). The deuteron wave function components ( u and w) have an inner node at the place of the hard core of the conventional realistic NN potentials.

Nuclear Matter Theory: A Status Report

Recent years have brought considerable improvement in the quality of both diagrammatic and variational many-body techniques. There appears to be general agreement that realistic NN potentials give a reasonable binding energy but an equilibrium density that is some 75% larger than the empirical value. Both conventional and chiral models of genuine manybody forces offer mechanisms for removing this discrepancy with each providing a simple picture for the required additional attraction for /rho/ < /rho//sub 0/. Neither approach is presently able to make a priori estimates of the magnitude of this effect with the delicacy required by the nuclear matter problem. Nor is it clear how to merge these pictures. We should not anticipate quick answers to these questions. One suitable interim strategy is to assume that many-body forces of the form suggested by either conventional or chiral pictures are responsible for the remaining discrepancy and to adjust parameters in such model many-body forces to restore agreement between theory and experiment. This might seem to be a summary dismissal of the standard nuclear matter problem. It should rather be regarded as revealing the next and richer layer of the nuclear matter problem.

Effects of NN and N Tensor Forces on -Separation Energy of 5He

The Λ5He wave function is solved variationally with a realistic NN potential and a ΛN potential including a tensor force. The NN and ΛN tensor forces reduce the Λ-separation energy BΛ for Λ5He by about 2.0 and 1.6 MeV, respectively. The BΛ-value calculated here is 2.4 MeV and is not larger than the experimental one. A main part of the overbinding problem in Λ5He is resolved by introducing the NN and ΛN tensor forces.

Photonuclear Sum Rule for Light Nuclei

The emhancement factor kappa in the electric dipole sum rule is calculated for A = 2,4,16 nuclei. Accurate solutions of the coupled Hartree-Fock, Bethe-Goldstone, and Bethe-Faddeev equations have been used for different realistic NN potentials. The need for measurements of the total cross sections, especially for /sup 4/He, is emphasized.

A variational approach to nuclear matter with realistic potentials

A lowest order constrained variational method for calculating the binding energy of nuclear matter, previously proposed by the present authors, is extended to treat the strong tensor force components of realistic NN potentials. Numerical results are given for three early potentials of Gammel, Christian and Thaler, and reasonable agreement is found with a previous calculation of Ristig, Ter Louw and Clark which included three-body cluster contributions to the energy. A range of five potentials giving good fits to the experimental two-body NN data is also studied, and binding energies of typically 22 MeV per nucleon at saturation densities corresponding to k F ≈ 1.6–1.7 fm −1, are found. For three of the potentials considered, comparison is made with the recent results of Pandharipande and Wiringa, which include the contributions to the energy from all of the most significant many-body clusters, and excellent agreement is found. It is suggested that explicit inclusion of some of the neglected internal degrees of freedom of the nucleons, such as the possibility of excitation to Δ (1236) states, might bring the equilibrium nuclear matter results closer to the empirical values.

Calculation of 3H, 3He properties with realistic NN-potentials in the hyperspherical basis

3H and 3He properties (the bound energy, the charge radius, S', P and D component weights and others) have been calculated using the Reid, Bressel-Kerman-Rouben and supersoft-core potentials.