Collective evolution of a parton in the vacuum: the ultimate partonic "droplet", non-perturbative QCD, and quantum entanglement.

In this talk we will discuss the non-perturbative QCD evolution of a single parton in the vacuum. We postulate that such a parton will develop the long-range collective effects of a multi-parton system, reminiscent of those observed in high-energy hadronic or nuclear interactions with large final-state particle multiplicity. Proton-Proton collisions at the Large Hadron Collider showed surprising signatures of a strongly interacting, thermalized quark-gluon plasma, which was thought only to form in collisions of large nuclear systems. Another puzzle observed earlier in e⁺e^- collisions is that production yields of various hadron species appear to follow a thermal-like distribution with a common temperature. We will begin this talk by proposing searches for thermal and collective properties of a single parton propagating in the vacuum using high multiplicity jets in high-energy elementary collisions. We will then present studies on several observables using the PYTHIA 8 Monte Carlo event generator. Experimental observation of such long-range collectivity will offer a new view of non-perturbative QCD dynamics of multi-parton systems at the smallest scales. Absence of any collective effect may offer new insights into the role of quantum entanglement in the observed thermal behavior of particle production in high energy collisions. Please see our paper at https://arxiv.org/abs/2104.11735.