Angular correlations between heavy quarks provide a unique probe of the quark-gluon plasma created in ultrarelativistic 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 þPb and pp collisions at the LHC. The muons are measured with transverse momenta and pseudorapidities satisfying pμ T > 4 GeV and jημj < 2.4, respectively. The distributions of azimuthal angle separation Δϕ for muon pairs having pseudorapidity separation jΔηj > 0.8, are measured in different Pb þPb 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, samesign charges, and all pairs. A clear peak is observed in all Δϕ distributions at Δϕ ∼ π, 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 Δϕ distributions, are found to not vary significantly as a function of Pb þ Pb collision centrality and are similar for pp and Pb þ Pb collisions. This observation will provide important constraints on theoretical descriptions of heavy-quark interactions with the quarkgluon plasma.

Aad, G., Abbott, B., Abeling, K., Abicht, N. ., Abidi, S. ., Aboulhorma, A., et al. (2024). Azimuthal Angle Correlations of Muons Produced via Heavy-Flavor Decays in 5.02 TeV Pb+Pb and pp Collisions with the ATLAS Detector. PHYSICAL REVIEW LETTERS, 132(20), 20230-1-202301-23 [10.1103/physrevlett.132.202301].

Azimuthal Angle Correlations of Muons Produced via Heavy-Flavor Decays in 5.02 TeV Pb+Pb and pp Collisions with the ATLAS Detector

Alfonsi, F.;Ballabene, E.;Bellagamba, L.;Bianco, G.;Boscherini, D.;Bruni, A.;Carratta, G.;Cremonini, D.;De Castro, S.;Fabbri, F.;Fabbri, L.;Franchini, M.;Gabrielli, A.;Giacobbe, B.;Lasagni Manghi, F.;Massa, L.;Monzani, S.;