Disentangling Sources of Momentum Fluctuations in Xe+Xe and Pb+Pb Collisions with the ATLAS Detector

Collaboration
Jul 8, 2024
23 pages
Published in:
  • Phys.Rev.Lett. 133 (2024) 25, 252301
  • Published: Dec 16, 2024
e-Print:
Report number:
  • CERN-EP-2024-173
Experiments:

Citations per year

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Abstract: (APS)
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 eventwise average transverse momentum [P([pT])]. Disentangling the contributions from fluctuations in the nuclear overlap size (geometrical component) and other sources at a fixed size (intrinsic component) remains a challenge. This problem is addressed by measuring the mean, variance, and skewness of P([pT]) in Pb208+Pb208 and Xe129+Xe129 collisions at sNN=5.02 and 5.44 TeV, respectively, using the ATLAS detector at the LHC. All observables show distinct features in ultracentral collisions, which are explained by a suppression of the geometrical component as the overlap area reaches its maximum. These results demonstrate a new technique to separate geometrical and intrinsic fluctuations, providing constraints on initial conditions and properties of the quark-gluon plasma, such as the speed of sound.
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