Physics delves into the mysteries of the universe, and one intriguing aspect explored at the Large Hadron Collider (LHC) is the creation of quark-gluon plasma during high-energy ion collisions. While heavy atomic nuclei were traditionally thought necessary for its formation, recent analyses from the LHCb experiment involving proton-proton and proton-ion collisions challenge this notion.
When heavy atomic nuclei collide at extreme energies in the LHC, a transient quark-gluon plasma emerges. This exotic state of matter, where quarks and gluons break free from their usual confinement in protons or neutrons, exists fleetingly. As the temperature decreases, quarks and gluons swiftly undergo hadronization, recombining to generate streams of secondary particles diverging at various angles.
The intricacies of the hadronization process, crucial for understanding the foundations of physical reality, remain enigmatic. Recent analyses from the LHCb experiment, featuring physicists from the Institute of Nuclear Physics of the Polish Academy of Sciences, offer new insights, shedding light on the quantum correlations between particles produced in collisions.
Hadronization unfolds in yoctoseconds—trillionths of one trillionth of a second—over femtometre distances, posing challenges for direct observation. Researchers infer the quark-gluon plasma's behavior by examining quantum correlations, focusing on Bose-Einstein correlations between pairs of pions or pi mesons.
In quantum mechanics, particles are described using wave functions, and the overlap of these functions leads to either Fermi-Dirac or Bose-Einstein correlations, the latter being of interest in this context.
The unique design of the LHCb detector allows physicists to examine particles emitted “forward” for the first time, completing the understanding of phenomena observed in other LHC experiments. Analyses encompassed small systems, including proton-proton, proton-ion, and ion-proton collisions, aiming to discern if collective phenomena associated with quark-gluon plasma in nucleus-nucleus collisions could manifest in smaller systems.
The findings suggest that quark-gluon plasma may be produced even in single proton collisions. Notably, sources of secondary particle emission in proton-proton collisions seem smaller than in mixed collisions. Observations of correlations in small systems spark discussions about their origin and potential connections with heavy-ion collisions. The interplay between correlations and particle angles in collisions further adds complexity to the puzzle.
Despite these advances, the true nature of quark-gluon plasma processes remains elusive. Theoretical models, currently phenomenological, require calibration with experimental data. Challenges persist, and further work lies ahead for physicists to unravel the intricacies of quark-gluon plasma and its role in the fundamental fabric of the universe.
Source: Polish Academy of Sciences