Two-particle number and transverse momentum balance function with event topology in pp collisions at $\sqrt{s}=13$ TeV

Abstract

The first study of charge-dependent two-particle differential number ($B$) and momentum balance functions ($P_2^{CD}$) 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 $\sqrt{s}=13$ 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 ($⟨N_{ch}⟩$) in relative pseudorapidity ($\Delta \eta$) and relative azimuthal angle ($\Delta \varphi$) with $|\eta |<2.4$ and $0.2<p_{\mathrm{T}}<2.0$ GeV. A narrowing of the balance function width is observed in $\Delta \eta$ and $\Delta \varphi$ 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 $⟨N_{ch}⟩$. 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 $P_2^{CD}$ as a quantitative handle on radial-flow-induced localization of charge-balancing pairs.

15 pages, 11 figures