Saturday 22 March 2025
Scientists have made a significant breakthrough in understanding the behavior of jets and their substructure in high-energy collisions, shedding light on the properties of the quark-gluon plasma (QGP), a state of matter thought to have existed in the early universe.
Jet energy-energy correlators (EEC) are a powerful tool for studying the internal structure of jets and the transition from perturbative to non-perturbative regimes of quantum chromodynamics (QCD). In high-energy collisions, partons (quarks and gluons) scatter and produce jets, which are collimated sprays of hadrons. The EEC measures the energy deposited by these particles as they interact with each other.
Researchers from the ALICE experiment at CERN’s Large Hadron Collider have analyzed data on jet production in pp collisions at a center-of-mass energy of 5.02 TeV. They found that the EEC distributions exhibit two distinct regions: a perturbative regime at large distances and a non-perturbative regime at small distances. This separation provides insight into the dynamics of jet formation, enabling the study of processes influenced by the type of initiating parton and the transition from perturbative splittings to the confinement of partons into hadrons.
The results show that the EEC is well described by a next-to-leading-logarithmic (NLL) pQCD calculation at large distances. However, as the distance decreases, non-perturbative effects become important, and the data deviates from the perturbative scaling. The small-distance region corresponds to later times in the jet evolution where partons evolve into hadrons.
The team also observed a peak in the intermediate distance region, which signals the transition from the perturbative to the non-perturbative regime. This turnover marks the point at which energy is uniformly distributed within the jet, resulting in purely combinatorial correlations among the EEC pairs, characteristic of freely moving hadrons.
Furthermore, researchers explored semi-inclusive jets in Pb-Pb collisions, where they analyzed the yield of charged-particle jets recoiling from a high-pT trigger hadron. They found that the yield suppression due to medium-induced energy loss is significant at low jet pT and falls below unity as the jet pT increases.
The results are compared to several model predictions, including JETSCAPE, JEWEL, and the Hybrid Model.
Cite this article: “Unveiling Jet Substructure in High-Energy Collisions: Insights into Quark-Gluon Plasma Properties”, The Science Archive, 2025.
Quark-Gluon Plasma, Jet Energy-Energy Correlators, Quantum Chromodynamics, Partons, Hadrons, Large Hadron Collider, Next-To-Leading-Logarithmic Pqcd, Non-Perturbative Effects, Perturbative Scaling
Reference: Haidar Mas’ud Alfanda, “Jet and jet substructure: ALICE results” (2025).
