To what extent is Gluon Confinement an empirical fact?

TL;DR

This paper investigates the empirical evidence for gluon confinement in QCD, analyzing experimental data to establish upper bounds on free-gluon production and discussing the distinction between quark and gluon confinement.

Contribution

It provides an analysis of experimental results to assess the empirical status of gluon confinement, offering bounds on free-gluon production in high-energy experiments.

Findings

No direct detection of free gluons in experiments

Established upper bounds on high-energy free-gluon production

Supports the hypothesis that gluons are confined in hadrons

Abstract

Experimental verifications of Confinement in hadron physics have established the absence of charges with a fraction of the electron's charge by studying the energy deposited in ionization tracks at high energies, and performing Millikan experiments with charged droplets at rest. These experiments test only the absence of particles with fractional charge in the asymptotic spectrum, and thus "Quark" Confinement. However what theory suggests is that Color is confined, that is, all asymptotic particles are color singlets. Since QCD is a non-Abelian theory, the gluon force carriers (indirectly revealed in hadron jets) are colored. We empirically examine what can be said about Gluon Confinement based on the lack of detection of appropriate events, aiming at an upper bound for high-energy free-gluon production.