  New predictions regarding the role of color flow in high energy Quantum
Chromodynamics (QCD) processes have emerged in the last decade. In particular,
the role of color flow is now being explored through many different
observables; one such observable is nearly back-to-back hadron correlations in
proton-proton collisions which are predicted to be sensitive to states that are
entangled via their QCD color charge. The PHENIX detector at the Relativistic
Heavy Ion Collider is well suited to study potential effects from color flow.
Angular correlations between nearly back-to-back hadrons or a direct
photon-hadron are measured to study the prediction of color entanglement or
factorization breaking. The correlations can be treated in a
transverse-momentum-dependent framework where sensitivity to non-Abelian
effects from color are predicted. These measurements are the first ever to
search for experimental evidence of these entangled states and will help
establish color flow in hadronic interactions as a new area of focus within QCD
research. Results are presented for proton-proton collisions at center-of-mass
energies of 200 and 510 GeV and proton-nucleus collisions at nucleon-nucleon
center-of-mass energies of 200 GeV. World measurements of processes where
factorization is predicted to hold are also compiled and analyzed to compare to
the new experimental results presented here. The measured results do not
indicate any obvious qualitative differences from observables where
factorization is predicted to hold. This indicates that quantitative
comparisons with phenomenological calculations will be necessary to identify
the magnitude of effects from color entanglement. As QCD is the only
non-Abelian quantum field theory known to exist in nature that admits bound
states, it will be essential to continue exploring unique QCD phenomena due to
color interactions in controlled ways in the coming years.

High Energy Physics - Experiment;Nuclear Experiment