Universality of multiparticle production in QCD at high energies

Abstract

By studying the color structure of multiparticle production processes in $\mathrm{p}+\mathrm{A}$-type (dilute-dense) collisions, we find that higher-point functions beyond typical dipoles and quadrupoles, e.g., sextupoles, octupoles, etc., naturally appear in the cross sections, but are explicitly suppressed in the large-${N}_{c}$ limit. We evaluate the sextupole in the McLerran-Venugopalan model and find that, in general, its analytical form cannot be written as combination of dipoles and quadrupoles. Within the color glass condensate framework, we present a proof that in the large-${N}_{c}$ limit, all multiparticle production processes in the collision of a dilute system off a dense system can, up to all orders in ${\ensuremath{\alpha}}_{s}$, be described in terms of only dipoles and quadrupoles.