Two-particle number and transverse momentum balance function with event-topology in pp collisions at √s=13 TeV

The first study of charge-dependent two-particle differential number (B) and momentum balance functions (P₂CD) with respect to an event shape variable, transverse spherocity, is reported. Results are presented from PYTHIA8 and EPOS-LHC model calculations in proton-proton (pp) collisions at √s = 13 TeV. To distinguish between back-to-back jet-like topologies and isotropic events, low and high transverse spherocity values are chosen. The correlation functions are measured as a function of averaged charged-particle multiplicity (Nch) in relative pseudorapidity ($Δη$) and relative azimuthal angle ($Δϕ$) with $|η| < 2.4$ and 0.2 < pT < 2.0 GeV. A narrowing of the balance function width is observed in $Δη$ and $Δϕ$ from low- to high-multiplicity collisions. Wider balance functions are found in isotropic events as compared to jet-like events. However, for the momentum correlations, a nearly flat dependence is observed with Nch. This study investigates charge conservation mechanisms and their correlations for events classified with jet-like and isotropic topologies. To isolate medium-driven effects, we compare EPOS-LHC with its hydrodynamic core enabled and disabled and observed narrowing patterns in B and P₂CD as a quantitative handle on radial-flow-induced localization of charge-balancing pairs.