Azimuthal angle correlations of muons produced via heavy-flavor decays in 5.02 TeV Pb+Pb and $pp$ collisions with the ATLAS detector

Abstract

Angular correlations between heavy-quarks provide a unique probe of the quark-gluon plasma created in ultra-relativistic heavy-ion collisions. Results are presented of a measurement of the azimuthal angle correlations between muons originating from semileptonic decays of heavy-quarks produced in 5.02 TeV Pb+Pb and $pp$ collisions at the LHC. The muons are measured with transverse momenta and pseudorapidities satisfying $p_{\mathrm{T}}^{\mu }>4$ GeV and $|{\eta }^{\mu }|<2.4$, respectively. The distributions of azimuthal angle separation, $\Delta \varphi$, for muon pairs having pseudorapidity separation $|\Delta \eta |>0.8$, are measured in different Pb+Pb centrality intervals and compared to the same distribution measured in $pp$ collisions at the same center-of-mass energy. Results are presented separately for muon pairs with opposite-sign charges, same-sign charges, and all pairs. A clear peak is observed in all $\Delta \varphi$ distributions at $\Delta \varphi \sim \pi$, consistent with the parent heavy-quark pairs being produced via hard-scattering processes. The widths of that peak, characterized using Cauchy-Lorentz fits to the $\Delta \varphi$ distributions, are found to not vary significantly as a function of Pb+Pb collision centrality and are similar for $pp$ and Pb+Pb collisions. This observation will provide important constraints on theoretical descriptions of heavy-quark interactions with the quark-gluon plasma.

33 pages in total, author list starting page 16, 4 figures, published as Phys.~Rev.~Lett.~132~(2024)~202301 All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2022-19

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