Dilepton Correlations from Heavy Flavor Decays

Abstract

Background: Azimuthal correlations between heavy flavor hadrons have been previously studied in $p+p$ collisions (Phys. Rev. C {\bf 98}, 034907 (2018), {\bf 101}, 034910 (2020)). These studies found good agreement with the data and provide a baseline for further studies in $p+A$ and $A+A$ collisions. Purpose: This work extends those studies to heavy flavor hadron decays to low mass lepton pairs. The low mass dilepton region is important for heavy ion collisions because of the interest in thermal dilepton production as a signature of the early time dynamics of the medium. Methods: Building on previous work, azimuthal correlations between leptons from semileptonic decays of heavy flavor hadrons are examined. The exclusive \textsc{HVQMNR} code is used in the calculations, made in the PHENIX acceptance at $\sqrt{s} = 200$~GeV and for dielectrons in ALICE at $\sqrt{s} = 13$~TeV. The $b \overline b$ decay contributions subtract like-sign lepton pairs from the opposite-sign signal. Results: The next-to-leading order calculations reproduce the trends of the PHENIX data. The calculations at 13~TeV show a change in signal as electron pair $p_T$ is increased, with the peak of the $\Delta \phi$ distribution moving from $\Delta \phi \sim \pi$ to $\sim 0$ and the contribution from bottom decays becoming dominant. The sensitivity of the signal to $k_T$ broadening is also studied and found to be small. Conclusions: It is found that the dependence on $k_T$ broadening previously observed is significantly reduced by the decay process. Despite this, the correlations between decay leptons retains some memory of the correlations between the parent hadrons in $p+p$ collisions. However, to study these correlations in heavy-ion collisions, it is necessary to separate them from thermal dilepton production in the same mass region.