J-dependence of the bootstrap mass spectrum. Comparison between the S-matrix bootstrap formalism and preceding semi-classical approaches

By working with the S-matrix formalism of the statistical-bootstrap equation, the possibility that the fireball average spin depends on the mass with a square-root behaviour (J approximately square root m/msub(π)) is investigated. This result is in partial agreement with the Hagedorn-Wambach and Chiu-Heimann models. Such behaviour is a particular case of a larger class which is analysed with a certain generality