One-nucleon Exchange Research Articles

A modified one-nucleon exchange model in π-N scattering

A modified version of the one-nucleon exchange model for π-N scattering which may satisfy the unitary sum rule associated with the partial wave dispersion relation is studied. It is shown that the model is compatible with the Froissart bound in the u-channel for l = 0 and l = 1. Using the N/ D technique the model haas been tested numerically for the l =0, T = 3 2 and l = 1, J = 3 2 , T = 3 2 waves. For the former a quantitative evaluation of the unability of the nucleon exchange approximation to give a correct prediction is given. For the latter it is shown that “exact” numerical solutions already given in the past do not satisfy the unitary sum rule. A new solution not suffering from this drawback is given and predicts qualitatively the (3, 3) resonance. Further improvements of it are suggested and the relevance of the unitary sum rule to study short-range forces is pointed out.

Inelastic electron-deuteron scattering with final-state interactions

Measurements of the cross sectiond2σ/dΩ dE′ for the inelastic electron-deuteron scattering processe+d→e+n+p have been used to determine the electromagnetic structure of the neutron. The effects on the theoretical cross section of the structure of the deuteron and of interactions between the outgoing nucleons are examined in detail. We start with the relativistic invariant expressions of the one-nucleon exchange diagram including deuteron structure to obtain the interaction Hamiltonian. For the disintegration near the quasi-elastic peak thed-n-p vertex function can be represented by nonrelativistic deuteron wave functions. The final state interaction is calculated from phenomenological nucleon-nucleon potentials. The rescattering corrections are found to lead to a decrease in the peak value of the cross section between −6% and −2% depending on the electron momentum transfer q2 which has been varied between 2.5f−2 and 40f−2. These corrections are largest for smallq2<5f−2. Furthermore the results show that the influence of our insufficient knowledge of the deuteron structure on the cross section is small.

Proton-Deuteron Elastic Scattering at High Momentum Transfers

Abstract : An experimental and theoretical investigation of proton-deuteron elastic scattering at high momentum transfers is presented. The differential cross sections for backward elastic scattering at incident proton kinetic energies of 1.0, 1.3, and 1.5 GeV were measured for four-momentum transfer squared (-t) from 2.6 to 5.0 (GeV/c)sq, which corresponds to cosine of center-of-mass proton scattering angles from -0.5 to -0.9. A backward peak is observed, and the slope and magnitude of the peak were determined. At 2.0 GeV for forward elastic differential cross section was measured for -t from 0.44 to 1.54 (GeV/c)sq. A shoulderlike departure from the forward diffraction peak was observed. The one-nucleon exchange peripheral model was successful in interpreting the backward peak. Calculations based on modern three-body quantum mechanical formalisms for the three-nucleon system supporting a two-body bound state also suggest the one-nucleon exchange process as the dominant mechanism. The measured forward differential cross section has been explained by the importance of double-scattering of the incident proton at higher momentum transfers. A negative value for the ratio of the real part to the imaginary part of the neutron-proton elastic scattering amplitude at 2.0 GeV is shown to yield maximum agreement with the experimental data. (Author)

One-Nucleon Exchange in Pion-Nucleon Scattering

We have studied the partial-wave amplitudes for pion-nucleon scattering in the approximation where the "driving force" comes from single-nucleon exchange. We start from the assumption that the amplitudes satisfy dispersion relations, but find that this is not enough to define a unique problem. Some restrictions upon the choice of amplitude to be inserted in the dispersion relations are found, but some ambiguities remain. Settling these in a "reasonable" way leads to the conclusion that the one-nucleon-exchange force is "too strong."