Initial state formation in the hydrodynamical theory of nucleon-nucleon collisions

Abstract

The treatment is based on the conjecture that in QCD, as in any theory of strong interactions, in many cases we have actually to deal with a continuous classical or quasiclassical medium (QCD vacuum, instantons) rather than with a pair-wise interacting particles. Meanwhile exactly this last approach is usually exploited when the parton (i.e. gluon and quark) interaction forms the basis of investigation of the possibility of formation of initial lump and estimating its size. Since actually the situation is far from being clearly perturbative we start from the opposite approximation, that of a continuous medium. Here viscosity is known to be essential. We estimate its role defining the necessary numerical parameter from ex-parimental data on transverse mass distribution of produced particles. The longitudinal size Δ of the initial lump for its succeeding isentropic hydrodynamical expansion turns out to be small (and decreases with CMS energy $\sqrt s \,as\,\left( {\sqrt s ^{ - 1/3} } \right)$ thus supporting the usual hydrodynamical theory applicability for the multiparticle production in nucleon-nucleon collisions.

Presented at the 6th International Conference on Ultra-Relativis-tic Nucleus-Nucleus Collisions — Quark Matter 1987, 24–28 August 1987, Nordkirchen, Federal Republic of Germany