2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/43835We propose that transverse momentum spectra with power-law tails observed in ultrarelativistic heavy ion collisions can be interpreted as originating in a medium in thermal equilibrium. General conditions on the dynamical equations are formulated, leading in equilibrium to various energy distributions of particles. Starting with the linear Fokker-Planck equation we analyze conditions for Boltzmann-Gibbs, Tsallis, or other equilibrium distributions based upon the dependence of fluctuation and dissipation on the energy of the observed subsystem. RHIC neutral pion data definitely exclude Boltzmann-Gibbs distribution over the entire range of observed transverse momenta.20 pages in preprint format incl. 3 figuresHigh Energy Physics - Phenomenologytext