Propagation of ''heat'' in hadronic matter

The space-time evolution of a local excitation hadronic matter (h.m.) is investigated in connection with the establishment of local thermodynamical equilibrium as assumed in statistical and hydrodynamical models. After a critical discussion of the concept of instantaneous equilibrium it is pointed out that peripheral reactions are a particularly useful source of information for the study of the fate of an excitation in h.m. A local excitation (''hot spot'') is considered corresponding to a pre-equilibrium phase and which is created in peripheral inelastic reactions with m/sub pi/ very-much-less-than q very-much-less-than p/subi/ where p/subi/ is the incoming momentum with m/sub pi/ very-much-less-than q very-much-less-than p/subi/ where p/subi/ is the incoming momentum of the projectile and q the momentum transfer. By solving the diffusion equation the distribution of the temperature field in the excited target (projectile) is obtained and all the relevant physical quantities such as average momenta of secondaries, multiplicities, and mass and energy distributions in semi-inclusive peripheral reactions are computed. It turns out that these quantities have a very pronounced angular dependence leading to a strong asymmetry in these observables. The measurement of this asymmetry can provide information on the constants of h.m. A discussion is presented how large p/sub perpendicular/ events observed in the CERN ISR energy range might be due to pre-equilibrium emission in close analogy to pre-equilibrium nuclear decay