On the Use of Transverse Momentum Spectra to probe Thermalisation and Collective Expansion in Relativistic Nucleus-Nucleus Collisions

Transverse momentum spectra of the reaction products from proton-proton and nucleus-nucleus collisions are discussed within the phenomenological frameworks of statistical phase-space and string fragmentation models. It will be shown that a string fragmentation model can accommodate all of the observations discussed here and consequently it is claimed that no conclusion about the thermal nature or collective expansion of the created system may be derived from observed transverse momentum spectra.