Nonperturbative factorization breaking and color entanglement effects in dihadron and direct photon-hadron angular correlations in $p$$+$$p$ and $p$$+$A collisions

TL;DR

This paper investigates color flow and potential factorization breaking in high-energy QCD processes through angular correlations in proton-proton and proton-nucleus collisions, aiming to identify signs of color entanglement effects.

Contribution

It presents the first experimental search for color entanglement effects in dihadron and photon-hadron correlations, providing new data to test QCD predictions about factorization breaking.

Findings

No obvious qualitative differences from factorization-predicted observables.

Results suggest the need for quantitative comparisons with phenomenological models.

First measurements of color entanglement effects in high-energy hadronic collisions.

Abstract

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.