Peter Signell

CHARACTERISTICS OF THE PROTON--PROTON INTERACTION DEDUCED FROM THE DATA BELOW 30 MeV.

Abstract A two-parameter description for each of the low energy 3P phase shifts is justified and used to perform the first comprehensive analysis of all of the proton-proton scattering data below 30 MeV. Particular attention is paid to magnetic moment, vaccuum polarization, and finite electromagnetic structure effects. Effective-range parameters for the 1S and 3P states are determined as well as possible, but distressing irregularities are noted in all of the data between 1 and 10 MeV. Nevertheless, some parameters are determined with precision, such as the singlet scattering length with a value of appE = − 7.822 ± 0.004 F. It is found that the central, tensor, and spin-orbit P-wave parameters reflect the uncertainties in the low energy data much more accurately than do the phase shifts themselves, and values of the parameters derived from experiment are given. The vacuum polarization interaction is shown to be present with a strength about equal to its theoretical value, but again with some irregularities. Finite electromagnetic structure effects deduced from the Hofstadter-Wilson dipole formula are found to be quite different from those found in previous calculations. The neutron-neutron scattering length, corrected for finite structure effects, is predicted to be ann = −17.06 F.

Model dependence of ann' PP Bremsstrahlung, and the binding energy of nuclear matter

Abstract Hard core, soft core, finite core, short range p2-dependent, and intermediate range p2-dependent potentials with one-pion-exchange tails are precisely matched to the 0-330 MeV 1S0 data. Adding the Hamada-Johnston potential for other states when necessary, predictions are made for the neutron-neutron scattering length, proton-proton bremsstrahlung, and the binding energy per nucleon in nuclear matter. Of these, only the nuclear matter binding energy shows significant model dependence.

Neutron‐proton measurements and phase shift analyses near 50 MeV

We report on our measurements of n‐p scattering observables at 50 MeV, most notably the recent measurement of the spin‐correlation parameter, Ayy. This measurement is sensitive to the phase shift parameters ?1 and δ (1P1), for which early phase shift analyses gave poorly determined or ’’unphysical’’ values. The results of our measurements are incorporated in a phase shift analysis to determine or ’’unphysical’’ values. The results of our measurements are incorporated in a phase shift analysis to determine current best‐fit values of 50 MeV n‐p phase shifts.

NN phase shift analysis, K‐matrix, and optimal polynomial theory

In this paper we discuss a new phase shift analysis and give some results for pp and np scattering. An improvement over the standard method of phase shift analysis is presented by the inclusion of the cut for 4mπ?t≲45mπ2. Unitarization is achieved through application of a K‐matrix formalism where we employ for the first time in NN, the ’’derivative amplitudes’’. We compare the theoretical predictions for the peripheral waves with the trends predicted by a new version of Optimal Polynomial Theory (OPT). With the analysis described here we aim at better determination of non‐peripheral phase shifts and a smooth transition between peripheral and non‐peripheral phases.

WHAT WE THINK WE KNOW ABOUT THE FREE NUCLEON-NUCLEON INTERACTION

The purpose of this talk is to show what we currently believe about the free NN system, and to compare it with what is actually being used in nuclear calculations. I will touch on four aspects: (i) present theory; (ii) the potentials produced by that theory as well as by NN experiment; (iii) the relevant NN amplitudes (phase shifts) and (iv) how to choose NN potentials and amplitudes for nuclear calculations.

THE NUCLEON-NUCLEON INTERACTION

This chapter discusses the use of NN potentials for nuclear physics calculations that were far from being phase-equivalent. The partial-wave-projections of the theoretical production amplitudes at the various energies gave the absorption coefficients needed for elastic-scattering data analyses. Due to inability to calculate higher exchanges, all calculations terminated after 2π or 3π exchange. Therefore, the resulting interaction was regarded as somewhat peripheral and the scattering phase shifts produced were not valid for low angular momenta or high energies. The π+π→π+π phase shift for a particular π π partial wave gave the phase of the same N N ¯ →π π partial wave. However, as the magnitude-squared of each N N ¯ →π π partial wave was all that enters into the NN interaction, the π π phase shifts disappear from the formalism. The partial-wave projections of the theoretical production amplitudes at the various energies gave the absorption coefficients needed for elastic-scattering data analyses.