Pion inclusive momentum distribution at 90° in a hydrodynamical model

We show that pion inclusive momentum distributions in $\mathrm{pp}$ collisions at 90° from 24 to 1500 GeV lab energies can be accounted for by a hydrodynamical model which has frame-independence symmetry and incorporates the evaporation phenomena. Within our solution, during its space-time development, the matter system only possesses a local thermal equilibrium but not a global equilibrium. The proper-time interval needed to achieve this equilibrium comes out to be comparable (with $c=1\mathrm{}$) to the longitudinal dimension estimated previously based on considerations of quantum statistical fluctuation.