Collectivity in hadron collisions

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The system size and energy scale dependence of many-body phenomena

Quantum Chromodynamics (QCD) predicts that at sufficiently high temperature and density, nuclear matter melts into fun- damental constituent particles and forms a Quark-Gluon Plasma (QGP). The important discovery that came from the experiments at RHIC and LHC was that the QGP created in large collision systems of gold or lead ions can be surprisingly well described by viscous hydrodynamics. The emergence of macroscopic fluid-like behaviour over distances much smaller than a single atom is a fascinating manifestation of the many-body physics of QCD in high-energy heavy-ion collisions (Berges et al., 2021).

The key experimental evidence which supports the existence of such a QGP fluid is the observed long-range multi-particle correlations or collective flows (see figure above). The pressure gradients in the QGP droplet accelerate the fluid, which creates correlations between the produced particle momentum. Because the collision produces a deformed QGP matter, this is then converted to momentum anisotropies in the final state. Remarkably, there is a growing body of evidence that such flow collective phenomena associated with QGP formation in heavy-ion collisions are universal and are found in all hadronic collisions, including proton-proton and proton-lead collisions, i.e., the so-called small systems. The key challenge in the field is to understand how different many-body phenomena depend on the system size and energy scale (see figure above).

I have taken a leading role in advancing state-of-the-art computations of nonequilibrium QCD using QCD effective kinetic theory (EKT). Together with collaborators, I identified and calculated the hydrodynamic, chemical, and thermal equilibration time scales of the QGP in large collision systems without transverse expansion (Kurkela & Mazeliauskas, 2019; Kurkela & Mazeliauskas, 2019). We developed practical tools to simulate the nonequilibrium evolution of the energy-momentum tensor, enabling detailed descriptions of heavy-ion collisions from the initial collision to the later hydrodynamic stages (Keegan et al., 2016; Kurkela et al., 2019; Kurkela et al., 2019). We discovered a novel far-from-equilibrium phenomenon involving time-dependent self-similar evolution of particle distribution functions and devised a method to calculate entropy production during the equilibration process in heavy-ion collisions (Mazeliauskas & Berges, 2019; Giacalone et al., 2019). Building on this work, our group is extending EKT studies, traditionally focused on large systems, to explore the emergence of collective behavior in small, transversely expanding collision systems (Kurkela et al., 2021).

References

2024

  1. Eur. Phys. J. C
    QCD challenges from pp to AA collisions: 4th edition
    Javira Altmann, and  others
    Eur. Phys. J. C, 2024
    DOI arXiv Cite
  2. JHEP
    Minijet quenching in non-equilibrium quark-gluon plasma
    Fabian Zhou, Jasmine Brewer, and Aleksas Mazeliauskas
    JHEP, 2024
    DOI arXiv Cite

2021

  1. Rev. Mod. Phys.
    QCD thermalization: Ab initio approaches and interdisciplinary connections
    Jürgen Berges, Michal P. Heller, Aleksas Mazeliauskas, and 1 more author
    Rev. Mod. Phys., 2021
    Abs DOI arXiv Cite
    230 InspireHEP citations
  2. JHEP
    Collective flow in single-hit QCD kinetic theory
    Aleksi Kurkela, Aleksas Mazeliauskas, and Robin Törnkvist
    JHEP, 2021
    DOI arXiv Cite
  3. Phys. Rev. C
    Predicting parton energy loss in small collision systems
    Alexander Huss, Aleksi Kurkela, Aleksas Mazeliauskas, and 3 more authors
    Phys. Rev. C, 2021
    DOI arXiv Cite
  4. Phys. Rev. Lett.
    Discovering Partonic Rescattering in Light Nucleus Collisions
    Alexander Huss, Aleksi Kurkela, Aleksas Mazeliauskas, and 3 more authors
    Phys. Rev. Lett., 2021
    DOI arXiv Cite

2019

  1. Phys. Rev. D
    Chemical equilibration in weakly coupled QCD
    Aleksi Kurkela, and Aleksas Mazeliauskas
    Phys. Rev. D, 2019
    DOI arXiv Cite
  2. Phys. Rev. Lett.
    Chemical Equilibration in Hadronic Collisions
    Aleksi Kurkela, and Aleksas Mazeliauskas
    Phys. Rev. Lett., 2019
    DOI arXiv Cite
  3. Phys. Rev. C
    Effective kinetic description of event-by-event pre-equilibrium dynamics in high-energy heavy-ion collisions
    Aleksi Kurkela, Aleksas Mazeliauskas, Jean-François Paquet, and 2 more authors
    Phys. Rev. C, 2019
    DOI arXiv Cite
  4. Phys. Rev. Lett.
    Matching the Nonequilibrium Initial Stage of Heavy Ion Collisions to Hydrodynamics with QCD Kinetic Theory
    Aleksi Kurkela, Aleksas Mazeliauskas, Jean-François Paquet, and 2 more authors
    Phys. Rev. Lett., 2019
    DOI arXiv Cite
    200 InspireHEP citations
  5. Phys. Rev. Lett.
    Prescaling and far-from-equilibrium hydrodynamics in the quark-gluon plasma
    Aleksas Mazeliauskas, and Jürgen Berges
    Phys. Rev. Lett., 2019
    DOI arXiv Cite
  6. Phys. Rev. Lett.
    Hydrodynamic attractors, initial state energy and particle production in relativistic nuclear collisions
    Giuliano Giacalone, Aleksas Mazeliauskas, and Sören Schlichting
    Phys. Rev. Lett., 2019
    DOI arXiv Cite

2016

  1. JHEP
    Initial conditions for hydrodynamics from weakly coupled pre-equilibrium evolution
    Liam Keegan, Aleksi Kurkela, Aleksas Mazeliauskas, and 1 more author
    JHEP, 2016
    DOI arXiv Cite
  2. Phys. Rev. C
    Fluctuations of harmonic and radial flow in heavy ion collisions with principal components
    Aleksas Mazeliauskas, and Derek Teaney
    Phys. Rev. C, 2016
    DOI arXiv Cite

2015

  1. Phys. Rev. C
    Subleading harmonic flows in hydrodynamic simulations of heavy ion collisions
    Aleksas Mazeliauskas, and Derek Teaney
    Phys. Rev. C, 2015
    DOI arXiv Cite