Paris Potential Research Articles

Baryons and a nucleon-nucleon potential in a colour-dielectric quark model with plain gluons

The quark model contains many-gluon degrees of freedom in the form of a colour-dielectric field χ and a colour interaction between quarks in the form of gluons without self-interaction (plain gluons). The confinement is due to the coupling of the many-gluon field x to the quark's mass. The quark mass is small inside a quark bag and gets infinitely large outside the bag. This leads to absolute quark confinement. We develop a non-relativistic version of the model and fit the mass and the root-mean-square radius of the nucleon. In addition we calculate an adiabatic nucleon-nucleon potential. It shows a short-range repulsion and an intermediate-range attraction between nucleons and is comparable to a Paris potential.

Faddeev calculations for low-energy p-d scattering.

The Coulomb-modified Faddeev equations were solved in momentum space for different separable potential models at ${\mathit{E}}_{\mathrm{lab}}^{\mathit{p}}$=2.5 and 3.0 MeV. The best agreement with available experimental data of zero- and first-order spin polarization observables was achieved by employing a separable approximation of the Paris potential in the calculation. These results, together with predictions of second-order p-d polarizations, demonstrate the necessity of a correct treatment of three-body Coulomb corrections. Moreover, no indication of model sensitivity is found in our results. Three-nucleon phase shift parameters are given and the validity of a simple approximate two-body description of the three-body Coulomb corrections is discussed.

Number-conserving sets and effective interactions through third order for mass-18 with the Bonn-Jülich potential

We have calculated the two third-order number-conserving sets of diagrams and the effective interaction through third order for 18O and 18F with the meson-theoretical Bonn-Jülich potential. All JT states of the (sd)2 configuration have been considered.The relative cancellation among the number-conserving sets is similar to that obtained with the meson-theoretic Paris potential, yielding therefore a somewhat improved cancellation compared to phenomenological potentials.The calculated spectra are compared to those obtained with the phenomenological Reid soft-core potential. The latter shows the best agreement with experiment whereas the Bonn-Jülich results agree poorly. Both potentials do however exhibit non-convergent behavior for certain low-lying 18F states. Some implications are discussed.

Analyzing power in neutron-proton scattering at 21.6 MeV

The analyzing power in neutron-proton elastic scattering at 21.6 MeV was measured using polarized neutrons from the 3H(d, n ) 4 He reaction. The results agree with recent measurements and with revised earlier data in the vicinity of 22 MeV. The combined data give Δ P LLS = (0.847 ±0.019)° and Δ D LS = (0.100±0.008)° and are consistent with predictions made from the Paris potential.

Np elastic scattering analyzing power characteristics at intermediate energies.

Recent measurements of charge symmetry breaking in the {ital np} system at 477 MeV, and of {ital A}{sub 00{ital nn}} for {ital np} elastic scattering at 220, 325, and 425 MeV also yield accurate analyzing power data. These data allow the energy dependence of the analyzing power zero-crossing angle and the slope of the analyzing power at the zero-crossing angle to be determined. The incident neutron energies span a region where the zero-crossing angle is strongly energy dependent ({ital E}{sub {ital n}}{lt}250 MeV) to where it is almost independent of energy ({ital E}{sub {ital n}}{gt}350 MeV). The results are compared to current phase-shift analysis predictions, recently published data, and the predictions of the Bonn and Paris potentials.

Effective interactions through third order for mass-18 nuclei with the Paris potential

We have studied the behavior of the effective interaction in the (sd)-shell through third order for mass-18 with the meson-theoretical Paris potential. All JT states are considered. The results are compared with those obtained with the G -matrix of Kuo and Brown, based on the phenomenological Hamada-Johnston potential. The excitation spectra obtained with both these potentials are rather similar, though the Paris potential gives a better fit through third order, whereas it produces more binding for low-lying states through second order. Still, evidence for non-convergent behavior is found in T =0 states for the Paris potential.

Differential cross section of the 2H(n, nnp)-reaction at En = 13 MeV

The differential cross section of the nD break-up reaction was investigated at E n = 13 MeV using the Erlangen multidetector neutron facility. Twenty-two different configurations including np final-state interaction, collinearity, coplanar- and space star were measured in a kinematically complete experiment. The results are compared with rigorous Faddeev calculations based on the Paris potential. The discrepancies between data and calculations indicate imperfections in the potential and may be caused by three-particle effects such as wrong off-shell behavior of the potential or an additional three-body force.

Full-folding-model description of elastic scattering at intermediate energies.

Nucleon-nucleus optical potentials are calculated using full off-shell nucleon-nucleon free t matrices based on the Paris potential. Applications to proton scattering from $^{40}\mathrm{Ca}$ at 200 and 300 MeV are presented. Significant differences are found between observables calculated using full-folding potentials and t\ensuremath{\rho} approximations to them, demonstrating the importance of an accurate treatment of off-shell effects. The agreement between calculated and measured observables improves substantially using the full-folding model.

Antiproton elastic scattering on even-even nuclei

Elastic scattering of antiprotons on even-even nuclei is calculated microscopically from the Dover-Richard and Paris potentials. The five different spin-dependent t-matrix elements are each parametrized in terms of simple functions. The fairly weak energy dependence is included by using an effective value of the relative energy obtained by averaging over the distribution in the nuclear tail. The first order optical potential reproduces reasonably well the differential cross section. The second order correction to the optical potential is then obtained in a perturbative treatment. Selfconsistency is only approximately satisfied, but we argue that the tremendous simplifications this entails are still sufficiently accurate for our purpose. Both the central and the spin-orbit optical potential, the differential cross section, the polarization and spin rotation functions are calculated. The spin dependence is significantly altered by the second order contribution. Simple analytical expressions are derived for medium effects and for the effect of various types of correlations. All experimentally available cases are investigated and very good agreement is found. We compare with previous work on this subject and discuss earlier conclusions in connection with our results.

Neutron-induced deuteron breakup cross section at 10.3 MeV.

The absolute cross section of n+d\ensuremath{\rightarrow}n+n+p at 10.3 MeV incident neutron energy has been measured in the so called ``space-star'' configuration. The results are compared with three-nucleon calculations based on the Paris potential and the new Bonn potential. The agreement within the experimental uncertainties of 8% puts an upper limit to the combined corrections due to relativistic effects, on-shell two-nucleon uncertainties, and the three-nucleon force.

Nuclear structure effects on the neutrinoless double beta decay

The nuclear matrix elements of the 0ν ββ decay of76Ge,82Se,100Mo,128,130Te,136Xe and150Nd are calculated in the proton-neutron quasiparticle RPA with theG-matrix of the Paris potential. It is shown that the matrix elements are not sensitive to details of nuclear structure, in contrast to the 2ν ββ decay. We investigate effects of ground-state correlations and those of short-range correlations on the suppression of the nuclear matrix elements. We also discuss effective values of the neutrino mass which are deduced from experimental 0ν ββ decay half-lives.

Few-body physics investigated through polarized neutron experiments in A ≤ 3 systems at TUNL

Accurate polarization data obtained with neutrons below 20 MeV in the A ≤ 3 systems provide important new information on details of the nucleon-nucleon (NN) interaction. The two-nucleon and three-nucleon data favor the Paris potential over the new Bonn (OBEPQ) potential. However, none of the realistic potential models describes the elastic neutron-deuteron analyzing power satisfactorily. Charge independence breaking in the 3P NN interactions and/or three-body force effects must be considered.

Zero degree cross section for the reaction 14C(p,n) 14N2.31, 14N3.95 at 200, 300, and 450 MeV.

We have measured the zero degree cross sections for the $^{14}(\mathit{p}$,n) reaction leading to the (2.31+3.95) MeV states in $^{14}\mathrm{N}$ at energies of 200, 300, and 450 MeV. Cross sections for the Fermi transition to the 2.31 MeV state and for the Gamow-Teller transition to the 3.95 MeV state have been extracted using earlier measurements of the cross-section ratios. The results are compared with calculations using G-matrix effective interactions based on the Paris potential, and on one of the Bonn potentials, and a t-matrix effective interaction derived from nucleon-nucleon phase shifts. The best fit to both the present results and earlier results at lower energies is provided by calculations based on the Bonn potential.

A microscopic analysis of antiproton-nucleus inelastic scattering at 600 MeV/c

Inelastic scattering of antiprotons to normal and non-normal parity states of 12C and 18O are studied in distorted wave g-matrix approximation. The aim is to investigate the success and failure of the Dover-Richard and Paris N N potentials in transition matrix elements. Theoretical results are compared to the available LEAR data at 600 MeV/ c. The Dover-Richard potential is generally more successful to explain data than the Paris potential.

Microscopic calculation of the temperature dependence of the effective interaction

The effective interaction between two nucleons inside nuclear matter is calculated microscopically for several densities and several temperatures, assuming it is given by the Brueckner g-matrix, derived from the separable Graz version of the Paris potential. Particular attention is paid to the temperature dependence and to the way of putting the effective interaction into a Skyrme functional. It is found that the latter task can be achieved with a very good accuracy and that the Skyrme coefficients are weakly and quadratically temperature dependent. The g-matrix issued from the Paris potential turns out to be rather different from the standard Skyrme forces in singlet odd states. The charge dependence is investigated through the study of neutron matter. The connection with the temperature dependence of the surface energy is also discussed.

Lambda-neutron interaction in kaon photoproduction from the deuteron.

The importance of hyperon-nucleon final-state interaction in kaon photoproduction from the deuteron is examined. By calculating the deuteron wave function using the Reid, Paris, or Bonn NN potentials, the uncertainty of this process due to the nucleonic wave function is found to be negligible. The insignificance of off-shell and relativistic effects is demonstrated by employing a completely relativistic wave function and comparing various approximations. We find the influence of the kaon production operator to be the most critical ingredient in this calculation. Final-state effects, which are included via a distorted-wave formalism, involve partial waves up to l=3. They produce a sharp rise of the cross section near threshold resulting in an enhancement by about a factor of 3, but diminish rapidly as the energy increases. Different \ensuremath{\Lambda}N potential models show variations of the effect by up to 10%.

Nucleon-induced deuteron breakup: Analysis of 14.1 MeV data by rigorous Faddeev calculations with meson-exchange NN interactions.

Kinematically complete breakup experiments for final-state interaction and collinear configurations have been analyzed by rigorous Faddeev calculations. The two-nucleon Paris potential and a one-boson-exchange parametrization of the new Bonn potential have been used. The treatment of charge-dependent forces in the Faddeev scheme is discussed and a simple (2/3-(1/3 rule is derived. In the collinear configuration a significant discrepancy is found between theoretical and experimental cross sections.

Rigorous Faddeev calculations for elastic neutron-deuteron scattering around 8 MeV c.m. energy

Rigorous Faddeev calculations of the cross sections and analysing powers for elastic nd scattering at E n = 10.0, 12.0, 13.0 and 14.1 MeV were made. As two-nucleon interactions we used the Paris potential and two OBE-parametrizations of the new Bonn potential. The nucleon-nucleon interaction was assumed to act in all partial waves with total angular momentum j⩽2. The influence of higher partial waves ( j = 3) and the charge dependence of the NN interaction in the 1S 0 wave were studied. Definite discrepancies between experiment and theoretical prediction for the neutron analysing powers were found.

Analyzing power for elasticn-d scattering at 13 MeV

The analyzing power for elasticn-d scattering was measured atE n=13 MeV. The result is in good agreement with experimental data atE n =12 MeV andE n =14.1 MeV. At backward angles the data are well above the predictions of a rigorous Faddeev calculation using the Paris potential.

Parity violation asymmetry in nucleon-nucleon scattering

We evaluate the helicity dependence of the differential and total cross section for the scattering of longitudinally polarized neutrons on unpolarized neutrons at E = 45 MeV following a SIN experiment and at E = 230 MeV in anticipation of an experiment at TRIUMF. (Both experiments study proton-proton scattering of course, namely p + p→ p+ p ). Calculations are based on the Desplanques, Donoghue and Holstein (DDH) theory for the weak NN interaction and on the Paris potential for the strong NN force. The results can be expressed as a linear combination in the (DDH) weak parameters h ρ 0, h ρ 2 and h ω 0, corresponding to exchanges of isoscalar ρ −, isotensor ρ −, and isoscalar ω − mesons, respectively. For the asymmetry in the total cross section we have found, using DDH suggested “best values”, A z (45 MeV) = −2.62 × 10 −7 and A z (230 MeV) = 0.07 × 10 −7. The small value of A z at 230 MeV is due to a sign change in the differential asymmetry. As for the asymmetry in the differential cross section we notice that even at the lower energy E = 45 MeV, the asymmetry in the differential cross section deviates from isotropy, since J > 0 weak amplitudes cannot be neglected.