Hydrodynamics and large transverse momenta in high-energy collisions

In high-energy multiproduction collisions, secondaries with transverse momentum ($p_T$) greater than a few times the pion mass have a $p_T$ distribution which falls off like a power of $p_T$. This has been interpreted as being due to nonhydrodynamic processes, e.g., constituent interchange or hard scatterings of partons. We show that, on incorporation of transverse expansion with appropriate boundary conditions, a Landau-type hydrodynamic model leads to a falloff like $p_T$ ${\mathrm{}}^{\mathrm{-}5}$ for relatively large transverse momenta ($p_T$∼a few GeV), contrary to popular expectations.