Realistic Nucleon-nucleon Potentials Research Articles

Duration and nonlocality of a nucleon-nucleon collision

For a set of realistic nucleon-nucleon potentials we evaluate microscopic parameters of binary collisions: a time duration of the scattering state, a mean distance and a rotation of nucleons during a collision. These parameters enter the kinetic equation as non-instantaneous and non-local corrections of the scattering integral, i.e., they can be experimentally tested. Being proportional to off-shell derivatives of the scattering T-matrix, non-instantaneous and non-local corrections make it possible to compare the off-shell behavior of different potentials in a vicinity of the energy shell. The Bonn one-Boson-exchange (A-C) and Paris potentials are found to yield very close results, while the separable Paris potential differs.

Benchmark calculations for polarization observables in three-nucleon scattering

High precision benchmark calculations for phase shifts and mixing parameters as well as observables in elastic neutron-deuteron scattering below the deuteron breakup threshold are presented using a realistic nucleon-nucleon potential. Two totally different methods, one using a variational principle in configuration space and the other solving the Faddeev equations in momentum space, are used and compared to each other. The agreement achieved in phase shifts and mixing parameters as well as in the polarization observables is excellent. The extreme sensitivity of the vector analyzing power A{sub y} to small changes of the phase shifts and mixing parameters is pointed out. thinsp {copyright} {ital 1998} {ital The American Physical Society}

3P2−3F2pairing in neutron matter with modern nucleon-nucleon potentials

We present results for the ${}^{3}{P}_{2}{\ensuremath{-}}^{3}{F}_{2}$ pairing gap in neutron matter with several realistic nucleon-nucleon potentials, in particular with recent phase-shift-equivalent potentials. We find that their predictions for the gap cannot be trusted at densities above $\ensuremath{\rho}\ensuremath{\approx}1.7{\ensuremath{\rho}}_{0},$ where ${\ensuremath{\rho}}_{0}$ is the saturation density for symmetric nuclear matter. In order to make predictions above that density, potential models which fit the nucleon-nucleon phase shifts up to about 1 GeV are required.

Tensor analyzing power Ayy of [formula omitted]-p radiative capture

Proton-deuteron radiative capture has been studied with polarized deuterons at a laboratory deuteron energy E d = 45 MeV. Precise data for the tensor analyzing power A yy have been measured in the angular range 50° to 160°. Three-nucleon Faddeev wave functions in the initial scattering and final bound state are calculated using realistic nucleon-nucleon potentials. Mesonic exchange currents are included according to Siegert's theorem. Comparison to other recent experimental data is performed as well.

Possible three-nucleon force effects in D–P scattering at low energies

We present measurements of the analyzing powers Ay and iT11 for proton-deuteron scattering at Ecm=432 keV. Calculations using a realistic nucleon-nucleon potential (Argonne V18) are found to underpredict both analyzing powers by 40. The inclusion of the Urbana three-nucleon interaction does not significantly modify the calculated analyzing powers. Due to its short range, it is difficult for this three-nucleon interaction to affect Ay and iT11 at this low energy. The origin of the discrepancy remains an open question.

Triton binding energies for modern NN forces and the π-π exchange three-nucleon force

We present high precision benchmark calculations for the triton binding energy using the most recent, phase equivalent realistic nucleon-nucleon (NN) potentials and the Tuscon-Melbourne pi-pi three-nucleon force (3NF). That 3NF is included with partial waves up to a total two-body angular momentum of j_max=6. It is shown that the inclusion of the 3NF slows down the convergence in the partial waves and j_max=5 is needed in order to achieve converged results within a few keV. We adjust the cut-off parameter Lambda in the form factors of the Tuscon-Melbourne 3NF separately for the different NN potentials to the triton binding energy. This provides a set of phenomenological three-nucleon Hamiltonians which can be tested in three-nucleon scattering and systems with A>3. A connection between the probability to find two nucleons at short distances in the triton and the effect of that 3NF on the triton binding energy is pointed out.

Ground-State Properties of 40Ca in Unitary-Model-Operator Approach with Realistic Nucleon-Nucleon Potentials

Ground-State Properties of 40Ca in Unitary-Model-Operator Approach with Realistic Nucleon-Nucleon Potentials

High-Precision Calculation of the Triton Ground State Within the Hyperspherical-Harmonics Method

The problem of calculating the three-nucleon bound-state properties in the case of realistic nucleon-nucleon potentials is studied by means of the hyperspherical-harmonics approach. Important aspects of the method are the inclusion of all relevant channels in the wave function and the use of large expansion bases. Results are presented for some of the local nucleon-nucleon potentials most frequently used. The conclusion is that, in these cases, the hyperspherical-harmonics approach allows at present for the results of highest precision. Moreover, the extension of the calculation technique to larger systems appears feasible and very promising.

Measurements of1H(d→,γ)3He and2H(p→,γ)3He at very low energies

Angular distributions of the analyzing powers iT{sub 11}, T{sub 20}, and T{sub 22} for {sup 1}H({rvec d},{gamma}){sup 3}He at 40{le}E{sub c.m.}{le}110 keV and the angular distribution of the analyzing power A{sub y} for {sup 2}H({rvec p},{gamma}){sup 3}He at 70{le}E{sub c.m.}{le}210 keV have been measured for the first time. In addition, absolute differential cross sections for proton-deuteron capture have been determined for E{sub c.m.}= 75, 108, 133, and 173 keV. Thick ice or heavy ice targets and two large-volume, high-purity Ge {gamma}-ray detectors were used. Results are in general agreement with an exact three-body calculation utilizing a realistic nucleon-nucleon potential. The vector-polarization observables are found to be especially sensitive to meson-exchange-current effects. The extracted S(0) value for proton-deuteron capture is {approximately}25{percent} lower than that presently used in astrophysical calculations. An expression for the thermonuclear reaction rate below 10 GK is given. {copyright} {ital 1997} {ital The American Physical Society}

Microscopic calculation of the 4He system

We report on a consistent, microscopic calculation of the bound and scattering states in the 4He system employing a realistic nucleon-nucleon potential in the framework of the resonating group model (RGM). We present for comparison with these microscopic RGM calculations the results from a charge-independent, Coulomb-corrected R-matrix analysis of all types of data for reactions in the A = 4 system. Comparisons are made between the phase shifts, and with a selection of measurements from each reaction, as well as between the resonance spectra obtained from both calculations. In general, the comparisons are favorable, but distinct differences are observed between the RGM calculations and some of the polarisation data. The partial-wave decomposition of the experimental data produced by the R-matrix analysis shows that these differences can be attributed to just a few S-matrix elements, for which inadequate tensor-force strength in the N - N interaction used appears to be responsible.

Meson and Quark Degrees of Freedom and the Radius of the Deuteron

The existing experimental data for the deuteron charge radius are discussed. The data of elastic electron scattering are inconsistent with the value obtained in a recent atomic physics experiment. Theoretical predictions based on a nonrelativistic description of the deuteron with realistic nucleon-nucleon potentials and with a rather complete set of meson-exchange contributions to the charge operator are presented. Corrections arising from the quark-gluon substructure of the nucleon are explored in a nonrelativistic quark model; the quark-gluon corrections, not accounted for by meson exhange, are small. Our prediction for the deuteron charge radius favours the value of a recent atomic physics experiment.

Determinations of the Neutron-Neutron Scattering Length a nn from Kinematically Incomplete Neutron-Deuteron Breakup Data Revisited

We review published analyses of the final-state-interaction enhancement observed in proton energy distributions obtained from kinematically incomplete neutron-deuteron breakup experiments. We compare the results derived from these analyses for the neutron-neutron scattering length, ann, with our results based on a rigorous treatment of the three-nucleon Faddeev equations in conjunction with the use of realistic nucleon-nucleon potentials. Our values for ann deviate outside the quoted uncertainties from the ones obtained in the previous analyses where simplified nucleon-nucleon interaction models were employed. In contrast to the previous determinations, the present results for ann are in clear disagreement with the values for ann based on π−-deuteron capture experiments. Unless inconsistencies in the experimental neutron-deuteron breakup data at low energies can be resolved and the neutron-deuteron breakup data at low energies can be resolved and the influence of possible three-nucleon-force effects can be reliably determined, we recommend that one not resort to the kinematically incomplete neutron-deuteron breakup reaction as a tool for determining a quantity as important for nuclear and particle physics as is the neutron-neutron scattering length ann.

Nucleon self-energies and spectral functions in nuclear matter at finite temperature with a realistic potential

We use a separable form of the Paris nucleon-nucleon interaction to calculate nucleon self-energies and spectral functions at the saturation density of symmetric nuclear matter at finite temperature. The behaviour of these quantities at temperatures above and close to the critical temperature for the superfluid phase transition in nuclear matter is investigated. From the self-energy the spectral function and occupation numbers at finite temperature are calculated. The sensitivity of the results for the realistic nucleon-nucleon potential to details of the interaction potential is studied by a comparison to an exploratory calculation previously done for the purely attractive Yamaguchi potential.

Low energy proton-deuteron versus neutron-deuteron breakup in four configurations: implications for Coulomb-force effects

Abstract We have measured cross sections of the pd breakup reaction at a laboratory proton energy of 10.5 MeV in four kinematically complete arrangements comprising space-star, collinearity, final-state interaction and quasi-free scattering conditions. We present our results and compare them to the predictions of rigorous three-nucleon Faddeev calculations using different realistic nucleon-nucleon potentials. We find cases of good agreement but also cases of clear discrepancies. The inclusion of the 2π-exchange Tucson-Melbourne three-nucleon force does not remove these discrepancies. Considering also pd data at 13 and 19 MeV and nd data at 10.5 and 13 MeV, we draw tentative conclusions about possible Coulomb-force effects in these configurations. In the quasi-free scattering, space-star, and collinear configurations, the Coulomb-force effects might possibly be responsible for at least part of the observed discrepancies. For the np FSI configuration the Coulomb-force effects are likely to be small.

Deuteron breakup reactionH2(p→,pp)ninduced by polarized protons atEp=19.0 MeV

We measured cross sections and vector analyzing powers of the breakup reaction $^{2}\mathrm{H}$(p\ensuremath{\rightarrow},pp)n at a laboratory proton energy of 19.0 MeV in four kinematically complete arrangements comprising space star, collinearity, final-state interaction, and quasifree scattering conditions. We present our results and compare them to the predictions of rigorous three-nucleon Faddeev calculations using different realistic nucleon-nucleon potentials. We found cases of good agreement but also cases of clear discrepancies. The inclusion of the 2\ensuremath{\pi}-exchange Tucson-Melbourne three-nucleon force does not remove these discrepancies but even worsens the description in all cases. In the quasifree scattering and space star configurations Coulomb-force effects might possibly be responsible for at least part of the observed discrepancies. \textcopyright{} 1996 The American Physical Society.

Three-Nucleon Charge Radius: A Precise Laser Determination Using3He

The isotope shift of the ${2}^{3}{S}_{1}\ensuremath{-}{2}^{3}{P}_{0}$ transition in helium has been measured using laser excitation of an atomic beam, yielding 33 668.074(5) MHz. This value, combined with atomic theory and the ${}^{4}$He nuclear charge radius, gives a ${}^{3}$He radius of 1.9506(14) fm. This result is over an order of magnitude more precise than previous determinations. It agrees with two recent theoretical values 1.958(6) and 1.954(7) fm from realistic nucleon-nucleon potentials and the ${}^{3}$He binding energy. Our result provides both a confirmation and a sensitive test of the nuclear theory of few-nucleon systems.

Tensor and vector analyzing powers of the 1H(,pp)n reaction

Abstract Tensor analyzing powers Axx and Ayy and vector analyzing powers Ay of the 1H( d ,pp)n breakup reaction at Ed = 52.1 MeV were measured in the symmetric collinear and coplanar-star kinematic configurations. The experimental results are compared with rigorous three-nucleon continuum calculations using realistic nucleon-nucleon potentials.

Hypervirial approach to calculating expectation values of the many-body Hamiltonian.

We present a new method, based on the hypervirial operator, for calculating expectation values of many-body Hamiltonians for local velocity-independent potentials. Our approach enables us to calculate the contributions of different components of an interaction [e.g., tensor, one pion exchange part (OPEP)] to the binding energy when {ital all} components are acting. In particular, using the integro-differential equation approach we investigate the contributions of different components of realistic nucleon-nucleon potentials to the triton and {alpha} particle ground-state binding energies. Although the tensor force contributes the most to the expectation value of the potential energy, we find that its overall contribution to the binding energy is much reduced by its large contribution to the expectation value of the kinetic energy.

Self-weakening of the tensor interaction in a nucleus.

We examine several ``landmarks'' for the effects of the tensor interaction on the properties of light nuclei. These were usually discussed in the context of small-space shell-model calculations. We show, using $G$ matrices derived from a realistic nucleon-nucleon potential, that when the model space is small (e.g., $0\hbar\omega$), these effects are overestimated, indicating that the tensor interaction is too strong. However, when larger spaces are used, there is a diminishing of these effects, which, in general, leads to better agreement with experiment.

Realistic Nucleon-Nucleon Potentials Expressed in Terms of the Gaussian Basis

Realistic Nucleon-Nucleon Potentials Expressed in Terms of the Gaussian Basis