J.A. Niskanen

On the energy levels in antiprotonic deuterium

Abstract The widths and level shifts of the 1S, 2P and 3D levels in antiprotonic deuterium are calculated using a separable NN potential based on the Dover-Richard scattering parameters.

The reaction p + p → d + π+ with a polarized beam and target

Abstract Using the method of coupled channels to incorporate NΔ intermediate states into the reaction p + p → d + π+ we calculate the differential cross sections, when both the beam and the target are polarized. The results for yy-polarized initial state are given in some detail at 580 MeV. We propose the use of the differential cross section with initial longitudinal polarizations to investigate the D-state probability of the deuteron, PD. This quantity is found to be very sensitive to PD.

NN scattering in the rearrangement model

Abstract The rearrangement model is used to derive a form for the N N annihilation potential. With the strength of this potential being essentially the only adjustable parameter, a good fit is possible, upto a p laboratory energy of 400 MeV, not only to the integrated total, elastic and charge exchange cross sections but also the backward angle differential cross section.

Phase equivalent interactions and dibaryon masses

Abstract Through a study of phase equivalent NN interactions with and without an explicit NΔ contribution we arrive at a simple prescription for effective NΔ thresholds with different relative orbital angular momenta. With only one exception these thresholds occur near the masses of the seven proposed I = 1 dibaryon resonances. The inference appears to be that those dibaryons are reflections of the opening of real NΔ channels.

Some improvements in the coupled channels calculations of the reaction p + p → d + π+

Abstract The reaction pp → d π + is investigated in a model which treats the important δ contribution by coupled channels. Among improvements over older similar calculations is e.g. a more exact treatment of the δ width by taking into account the kinetic energy of the spectator nucleon. Also the pion s-wave rescattering is given an energy dependence more adequate outside the threshold region. Agreement with data up to at least 600 MeV is good and results are shown at 580 MeV where the most extensive data exist. It is proposed that this reaction could be used to determine the transition potential NN → N δ .

A new dynamic selection rule for pp into two mesons

Abstract We show that quark-antiquark annihilation into gluons gives a suppression of p p annihilating into π±ϱ+- from p p 1S0 and 3P states at threshold.

pp Annihilation into two mesons using the 3P0 model

Abstract The N N optical potential due to annihilation into two mesons is derived. The model is based on quark-antiquark rearrangement plus a single quark-antiquark annihilation into the vacuum. The imaginary part of the optical potential is dominated by the N N (13P0) component and results in a central p p potential that is considerably weaker than that of Dover and Richard.

The differential cross section and polarization in p + p → d + π+

Abstract The formalism originally developed for incorporating NΔ-configurations into the mechanism for the production of p-wave pions is now extended to s- and d-wave pions. The differential cross section and the polarization asymmetry are calculated for laboratory energies ranging from threshold to 750 MeV.

p + p → d + π+ p-wave production

Abstract The production of p-wave pions in p + p → d + π + is calculated by introducing into the initial wavefunction NΔ configurations consistent with elastic scattering. Reasonable agreement with experiment is obtained without further adjustment. The Galilean term has only a small effect.

An extension of the 13P0 model for qq̄ annihilation

Abstract It is shown that a natural extension of the 13 P 0 model for qq annihilation introduces effects that are essentially indistinguishable from those usually attributed to the 13 S 1 component of the gluon exchange model e.g. NN(S-wave) → πϱ.