The phenomenological analysis of hadronic multiplicity distributions

The aims of the present paper are limited to a description of theoretical and phenomenological techniques which are, as far as possible, model independent, or at least valid for a class of models. It is the authors' experience that most of the gross measures of particle reaction data (e.g. total cross sections, inclusive distributions, KNO ''plots,'' etc.) do not discriminate among models unless supplemented with more fine grained information, especially correlations of various kinds. In the absence of a quantitative theory for the exclusive matrix elements, from which all else follows, it seems more constructive to work from the outside to the inside. (An especially powerful tool for this is intensity interferometry, much used in the statistical theory of optics but as yet rather undeveloped for the analysis of elementary particle data.) Whenever possible we emphasize the statistical essence of an observable, which can be rather independent of the particular dynamical process. A familiar example is the Maxwellian energy distribution of gas molecules in thermal equilibrium, whose form (as does the validity of hydrodynamic equations for the system) is independent of the detailed force law. This example illustrates both the strength and weakness of the approach