abstract

A unified description of diffractive production processes on nucleons and nuclei based on a model proposed some time ago by Białas, Kotański and the author is discussed.

abstract

In these lectures some experimental methods useful for detecting coherent processes are compared. Experimental results of coherent production by \(\pi \) and \(K\) mesons are discussed. High statistics results were obtained from a counter experiment performed at CERN. The optical model for multiple scattering is shown to fit the data of 3\(\pi \), 5\(\pi \), and \(K\pi \pi \) production very well, while some doubts as to its application to \(K^*\)(890) production remain. The main results of the analysis are the following. The absorption of 3\(\pi \) and 5\(\pi \) systems in nuclear matter is small; it corresponds to a total cress-section \(\sigma \approx 25\) mb. Mass distributions of 3\(\pi \), 5\(\pi \) and \(K\pi \pi \) show broad structureless peaks. Both 3\(\pi \) and \(K\pi \pi \) are almost 100% two-body systems with \(\pi \varrho \) and \(\pi f\) for 3\(\pi \) and \(K^*(890)\pi \) in \(K\pi \pi \) (no \(K\varrho \) observed). The 3\(\pi \) Dalitz plot distributions show structure within the \(J^P = 1^+\) amplitude, possibly \(S\)–\(D\) interference of the \(\pi \)–\(\varrho \) state. The production cross-section of 3\(\pi \) on a nucleon, deduced from a fit over nine target elements, seems to rise by 30% from 9 to 15 GeV, while the absorption in nuclear matter appears unchanged. Coherent production of \(K^*\)(890), a non-diffractive process, is clearly observed. A model for this process including Coulomb production, strong production, and their interference, is discussed. A fit to 10 data points, the integrated coherent production cross-sections on five elements and three beam momenta, gives \(0 \lt {\mit \Gamma }(K^* \to K\gamma ) \lt 80\) keV.

abstract

Diffractive dissociation of pions, kaons and nucleons is reviewed, and the data are compared with elastic scattering. Similarities in the final states are stressed, and the important role of off-mass-shell \(\pi \)-hadron scattering in diffractive dissociation is emphasized. Several new experimental techniques employed in the study of diffractive processes are discussed.

abstract

This is a review of the theory of coherent nuclear production of multi-body states having a broad mass spectrum. Two kinds of phenomena at e of central interest: the production of broad enhancements such as \(A_1\) and \(Q\), and inclusive spectra in very high energy hadron-nucleus collisions. The major topics discussed are: (1) the very interesting and informative inclusive spectra that are expected to result from nuclear collisions if diffraction dissociation plays a major role in the underlying hadron-hadron collisions; (2) a theory of coherent production that allows for strong coupling between the elastic and coherent production channels, the longitudinal momentum transfer, and changes of mass resulting from successive diffractive collisions within the nucleus; (3) Van Hove’s model for explaining the astonishingly small total cross-sections that have been extracted from multi-boson production experiments, and the questions raised thereby concerning the structure of the amplitudes that describe the scattering of the produced states by a system of nucleons.

abstract

Two important aspects of the isospin analysis of hadronic diffractive production processes are discussed. They are (1) cross-channel isospin representation, and (2) isospin analysis of “integrated cross-sections”. Examples are taken from single pion production in \(\pi N\) and \(NN\) collisions, and graphical illustration of the results are presented.

abstract

The Ascoli method for the partial wave analysis of the 3\(\pi \) system produced diffractively is discussed. The tests of the factorization assumption are proposed. It seems that the most efficient test is to compare the density matrix elements for events in various regions of the Dalitz plot.

abstract

The experimental situation concerning helicity conservation in diffractive processes is reviewed. As an introduction a short repetition of the necessary formulae of the helicity formalism is carried out. The tests for helicity conservation are then derived and the corresponding experimental data are discussed. The results are the following: \(s\)-channel helicity conservation seems to hold for elastic diffraction scattering (I include here the photoproduction of the \(\varrho \)-meson), but nearly all inelastic diffractive processes show small deviations from \(t\)-chanel helicity conservation.

abstract

In these lectures I want to consider diffractive production reactions with very close attention to the constraints that experimental data at accelerator energies (say below 30 GeV/\(c\)) imposes on any relevant theory. Because of three “problems” I argue that most of the traditional views of diffractive production are of limited value in describing the actual data. These problems are (i) The existence of crossovers for diffractive production, which implies contributions which change sign between processes such as \(Kp \to Q^0p\) and \(Kp \to {\overline Q}_0p\), or \(\pi ^{\pm }N \to A_1^{\pm } N\); (ii) Miettinen and Pirilä have recently pointed out that the dramatic decrease in production momentum transfer slope with increasing \(M^2\) must be a property of the matrix element rather than induced by kinematic effects, but the traditional models for diffractive production generally have a constant slope in the matrix elements; (iii) Detailed arguments concerning sizes of diffractive cross-sections as compared with non-diffractive ones. The form which a model capable of describing the data might take is indicated by constructing an example. It uses important contributions from a number of the available \(s\)-channel helicity amplitudes, with \(t\) dependences analogous to those found in conventional two-body reactions. In addition to allowing us to describe all the qualitative features of the data, the model suggests an interpretation of \(t\)-channel helicity “conservation” and shows how to predict the helicity properties of the reaction from the shape of the differential cross-section. A brief discussion is given of the energy dependence of resonances and background in the diffractive mass spectrum.

abstract

General features of diffractive dissociation in inclusive reaction are discussed especially in the case when it dominates the high energy total cross-section.

abstract

The Böhm, Joos, Krammer [DESY preprint 72/11] relativistic quark model is used to obtain high energy meson scattering amplitudes from quark–quark elastic (absorptive) scattering amplitudes. A relativistic form of Glauber’s multiple scattering expansion is assumed and some results reported.

abstract

Arguments are given that the traditional, Glauber-like model for the multiple scattering of composite objects be modified to the extent of including relativistic deformation of the wave functions. It is argued that this modified formalism is a specific realization of Van Hove’s model of coherent nuclear production of multi-body states and thus is sufficient to explain the astonishingly small nucleon total cross-sections that have been extracted from multi-boson production experiments. It is shown on the simple example of Lorentz-contracted oscillator wave functions that, to have Van Hove’s effect present, the interaction between the components of the diffractively produced object must be of the order of magnitude of their masses.