ATLAS Heavy Ion Group

ATLAS Heavy Ion Group
Name	ATLAS Heavy Ion Group
Formation	1990s
Headquarters	CERN
Region served	Worldwide
Parent organization	ATLAS Collaboration

ATLAS Heavy Ion Group

The ATLAS Heavy Ion Group is a research cohort within the ATLAS Collaboration at CERN devoted to heavy-ion collisions and high-density Quantum Chromodynamics. The group participates in experiments at the Large Hadron Collider and interfaces with institutions such as Brookhaven National Laboratory, Lawrence Berkeley National Laboratory, Fermi National Accelerator Laboratory, SLAC National Accelerator Laboratory, and universities like University of Oxford, University of Cambridge, University of Tokyo, University of Chicago, and MIT. Members collaborate with experiments including ALICE (A Large Ion Collider Experiment), CMS Experiment, LHCb and with theory centers such as Institute for Nuclear Theory, Perimeter Institute, Nordita, CEA Saclay, IHEP Beijing and INFN sections.

Overview

The group focuses on analyzing lead–lead and proton–lead collisions at the Large Hadron Collider and comparing results with data from the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, the SPS (Super Proton Synchrotron) legacy measurements, and results from experiments like PHENIX, STAR, NA61/SHINE, and WA98. It integrates detector expertise from collaborations that built parts of the ATLAS detector such as the Inner Detector (ATLAS), Calorimeter (ATLAS), Muon Spectrometer (ATLAS), and the Trigger and Data Acquisition (TDAQ) systems, as well as simulation tools like GEANT4, PYTHIA, HIJING, AMPT, and HYDJET.

Research Program and Physics Goals

The research program aims to study quark–gluon plasma formation, thermalization, and collective flow using observables like jet quenching, heavy-flavor suppression, quarkonium production, and azimuthal anisotropies. Analyses connect to theoretical frameworks including Quantum Chromodynamics, Hydrodynamics (physics), AdS/CFT correspondence, Color Glass Condensate, and lattice studies from CERN Theory Division and institutions like Brookhaven National Laboratory and BNL. Targets include measurements of nuclear modification factors, elliptic flow coefficients, ridge correlations, and charmonium and bottomonium states such as J/ψ, ψ′, Υ(1S), Υ(2S), and Υ(3S), employing comparisons to predictions from groups at Lawrence Berkeley National Laboratory, Institute for High Energy Physics (IHEP), National Institute for Nuclear Physics (INFN), and Institut de Physique Théorique.

Detector Upgrades and Experimental Techniques

The group has contributed to upgrades of pixel detectors including the Insertable B-Layer and the ATLAS Inner Detector refurbishment, calorimeter timing improvements, and muon system enhancements using technologies championed by CERN groups and national labs like KEK, DESY, TRIUMF, CEA, and University of Manchester. Techniques involve heavy-ion specific triggers developed with the TDAQ team, pileup mitigation methods based on algorithms from ATLAS computing, and machine learning tools implemented with software libraries used at CERN OpenLab and industry partners. They exploit jet reconstruction algorithms like anti-kT from FASTJET and grooming methods developed in association with theorists at SLAC, Harvard University, Princeton University, Stanford University, and Columbia University.

Key Results and Publications

Key publications report observations of jet quenching phenomena, long-range two-particle correlations (the "ridge"), and differential suppression of quarkonia, with results compared to RHIC experiments such as PHENIX and STAR. Major peer-reviewed articles have appeared in journals and proceedings associated with organizations like Physical Review Letters, Journal of High Energy Physics, Physics Letters B, and collaborations with authors from CERN, University of California, Imperial College London, University of Pennsylvania, Yale University, and Peking University. Landmark results include measurements of high-pT charged particle suppression, modification of jet fragmentation functions, heavy-flavor electron and muon yields, and centrality-dependent flow harmonics, often in joint analyses with CMS Experiment and ALICE (A Large Ion Collider Experiment) teams.

Collaboration and Organization

The group functions within the governance of the ATLAS Collaboration with representation on physics and performance boards, hardware groups, and publication committees. Institutional members span national laboratories and universities such as CERN, Brookhaven National Laboratory, Lawrence Berkeley National Laboratory, Fermilab, KEK, DESY, INFN, CEA, University of Oxford, University of Cambridge, Imperial College London, University of Tokyo, Peking University, Tsinghua University, University of Toronto, McGill University, and University of Melbourne. Coordination involves working groups for jet physics, heavy-flavor, quarkonium, flow, and soft probes, interacting with theory collaborations at INT and experiment counterparts at ALICE (A Large Ion Collider Experiment) and CMS Experiment.

Outreach and Education

Members engage in outreach through public lectures at CERN, participation in masterclasses organized with the International Particle Physics Outreach Group, contributions to educational programs at universities like University of Oxford, University of Cambridge, University of Tokyo, and summer schools such as CERN Summer Student Programme, Les Houches School of Physics, and SERC Summer School. They produce materials for initiatives including European Research Council events, science festivals in cities like Geneva and London, and collaborations with museums such as the Science Museum, London and Musée d'Histoire des Sciences (Geneva).

Future Directions and Planned Experiments

Planned directions include participation in high-luminosity heavy-ion runs at the High-Luminosity Large Hadron Collider, detector upgrades coordinated with HL-LHC projects, precision studies of small-system collectivity in proton–lead and proton–proton collisions, and synergy with future facilities like the proposed Electron-Ion Collider at Brookhaven National Laboratory. Forward physics programs will interface with projects at LHCb and forward detector proposals, while theoretical collaborations include work with Institute for Nuclear Theory, Perimeter Institute, and CERN Theory Division to refine descriptions of strongly coupled Quantum Chromodynamics matter.

Category:Particle physics collaborations