abstract

We discuss the role played by charged pion pairs in mediating high energy, forward Compton scattering, \(\varrho ^0\) meson photoproduction and \(\varrho ^0\) meson elastic scattering. With nucleon targets we find deviations from the “\(\varrho ^0\)-photon analogy” theory relating these interactions, primarily in the real parts of the amplitudes. Generalizing to nuclear targets, we take into approximate account the multiple scattering of a pion pair as well as that of the \(\varrho ^0\). We discuss why the quantities appearing in the conventional, Glauber multiple scattering theory of these reactions require some reinterpretation.

abstract

The general ideas of the Good and Walker diffraction dissociation mechanism are reviewed and a proposal of a specific realization of these ideas is presented. The model, developed by Czyż, Kotański and myself, is based on the idea that the interacting particles should be considered as fluctuating objects. During the collision process these virtual fluctuations become real observable states. Thus, the model can be viewed as a generalization of the vector dominance model of \(\varrho \) photoproduction. The model explains all essential features of diffractive production and it provides many important tests, particularly for the diffractive production from nuclei.

abstract

We review data on coherent production reactions from nuclei in \(\pi \), \(K\), nucleon and antinucleon beams of momenta above \(\sim 2\) GeV/\(c\). Characteristics of the dominant (“vacuum exchange”) reactions and rarer (“\(\omega \) exchange”) reactions are summarized.

abstract

The optical formulation of high energy coherent reactions of elementary particles (elons) with nuclei is derived in an heuristic manner, which nevertheless competes in rigor with extant presentations of the subject. The formalism is applied to elastic scattering on nuclei, including the possibility of collective low-lying nuclear excitations. Coherent production of \(\varrho \) and \(A\) mesonic states is discussed. Reliability of the nucleus as a measuring tool for elon attenuation is emphasized, and many corrections to the simplest approximation are examined. An approximate treatment of inelastic shadowing is given, and the speculation put forth that at very high energies there might be eigenstates of indefinite multiplicity which suffer anomalously low attenuation in nuclear matter.

abstract

The eikonal approximation for the contributions to inelastic scattering from arbitrarily crossed ladder graphs is considered. The particle represented by one of the “side-pieces” of the ladders is allowed to change its state and mass at each rung; the other side-piece particle is restricted to have at most one change of state, and that only if its elastic interactions are the same in the two states. When the denominators of the latter side-piece can be linearized the amplitudes reduce to forms essentially identical to those found in non-relativistic coupled-channel potential theory. This result is independent of the ratio of the energy to the side-piece mass and connects smoothly the non-relativistic and extreme relativistic regimes. Its implications for absorptive models are discussed briefly.

abstract

The following processes were discussed: The coherent bremsstrahlung emission of photons by electrons at \(\sim 1000\) GeV. The \(\sigma _{\rm coh}\)-energy dependence for \(3\pi \)- and \(5\pi \)-production by pions in the energy interval 17 GeV–200 GeV. Interaction of pionic systems produced at very high energy with nucleons inside the nucleus.

abstract

The general analysis of electron excitation of nucleon resonances is presented, and the consequences of two very simple models of the nucleon are discussed. The results are compared with SLAC data on this process.