Many-body QCD phenomena in high-energy proton and nuclear collisions

• Applicant: Dr. Aleksas Mazeliauskas
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 496831614

The emergence of macroscopic medium properties over distances much smaller than a single atom is a fascinating manifestation of strong interactions among elementary particles in high-energy nuclear collisions. The observation of collective particle behaviour in collisions of heavy ions (gold or lead) at the Relativistic Heavy Ion Collider at BNL and the Large Hadron Collider at CERN is strong evidence that a new exotic phase of matter called the Quark-Gluon Plasma is created in these relatively large collision systems. However, the striking discovery of the very same collective phenomena in much smaller systems of proton-proton and proton-lead collisions at the LHC has confounded physics expectations. The recent community recommendation for the European Strategy for Particle Physics emphasized that the main physics goal of future experiments with heavy-ion and proton beams at the LHC is a detailed, experimentally tested dynamical understanding of how out-of-equilibrium evolution occurs and equilibrium properties arise.Uncovering the physical origins of collective behaviour in all hadronic collisions and explaining their dependence on the size of the collision system is the main goal of this project.A) As the core part of the project, I will use my expertise on QCD thermalisation and, in particular, QCD effective kinetic theory to build a comprehensive model of emergent phenomena in small systems. My group will then model and predict the rich set of kinematic (integrated and momentum differential), chemical, and electromagnetic signals of collective phenomena that have been observed at the LHC in collision systems with different size.B) In parallel I will do perturbative QCD calculations of high momentum transfer processes in nuclear collisions to design sensitive tests for yet undiscovered medium-induced phenomena in small systems.As the result of these activities my group will construct a detailed theoretical picture of microscopic QCD equilibration in proton and nuclear collisions.

• DFG Programme: Independent Junior Research Groups