Disentangling sources of momentum fluctuations in Xe+Xe and Pb+Pb collisions with the ATLAS detector

Abstract

High-energy nuclear collisions create a quark-gluon plasma, whose initial condition and subsequent expansion vary from event to event, impacting the distribution of the event-wise average transverse momentum ($P([p_{\mathrm{T}}])$). Distinguishing between contributions from fluctuations in the size of the nuclear overlap area (geometrical component) and other sources at fixed size (intrinsic component) presents a challenge. Here, these two components are distinguished by measuring the mean, variance, and skewness of $P([p_{\mathrm{T}}])$ in ${}^{208}$Pb+${}^{208}$Pb and ${}^{129}$Xe+${}^{129}$Xe collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ and 5.44 TeV, respectively, using the ATLAS detector at the LHC. All observables show distinct changes in behavior in ultra-central collisions, where the geometrical variations are suppressed as the overlap area reaches its maximum. These results demonstrate a new technique to disentangle geometrical and intrinsic fluctuations, enabling constraints on initial condition and properties of the quark-gluon plasma, such as the speed of sound.

34 pages in total, author list starting page 17, 7 figures, no tables. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2021-20/

References in corpus (6)

• Glauber Modeling in High Energy Nuclear Collisions
• Triangularity and Dipole Asymmetry in Heavy Ion Collisions
• Event-by-event mean $p_{\mathrm{T}}$ fluctuations in pp and Pb-Pb collisions at the LHC
• Transverse-momentum fluctuations in relativistic heavy-ion collisions from event-by-event viscous hydrodynamics
• Measurement of the azimuthal anisotropy of charged-particle production in Xe+Xe collisions at $\sqrt{s_{\mathrm{NN}}}=5.44$ TeV with the ATLAS detector
• Collision Energy Dependence of $p_{\mathrm{t}}$ Correlations in Au+Au Collisions at RHIC

Cited by in corpus (8)

• Imaging nuclear shape through anisotropic and radial flow in high-energy heavy-ion collisions
• Feasibility of measuring the speed of sound of the quark-gluon plasma from the multiplicity and mean $p_T$ of ultracentral heavy-ion collisions
• The size of the quark-gluon plasma in ultracentral collisions: impact of initial density fluctuations on the average transverse momentum
• Bayesian reconstruction of anisotropic flow fluctuations at fixed impact parameter
• Extracting the speed of sound of QCD from transverse momentum fluctuations
• High-order fluctuations of temperature in hot QCD matter
• Kinematic and dynamical origins of mean-$p_T$ fluctuations in heavy-ion collisions
• The collectivity of transverse momentum fluctuations