Jet-associated Balance Functions of Charged and Identified Hadrons in pp Collisions at $\sqrt{s}=13.6$ TeV using PYTHIA8

TL;DR

This work investigates hadronization and possible collective-like dynamics inside jets produced in pp collisions at $\sqrt{s}=13.6$ TeV by analyzing jet-frame charge balance functions for inclusive and identified hadrons. Using PYTHIA8 with CP5 and a new color reconnection tune, the study reveals that balance-function widths in $\Delta\eta^{*}$ and $\Delta\phi^{*}$ narrow as jet multiplicity increases, with a pronounced species dependence linked to strangeness production and baryon-number transport. The azimuthal narrowing is particularly sensitive to color reconnection, suggesting multiparton interactions and CR contribute to jet-scale collectivity-like features, especially in high-multiplicity jets. The high-$p_T$ regime inside jets shows fragmentation-dominated correlations with minimal multiplicity dependence, establishing particle-identified balance functions as a sensitive, flavor-resolved probe of hadronization and small-system dynamics. Overall, the results provide stringent constraints for hadronization models and motivate future measurements to explore collectivity signatures in small systems.

Abstract

We present a study of charge balance functions inside jets in proton-proton collisions at $\sqrt{s}=13.6$ TeV using the PYTHIA8 event generator. The balance function is a differential observable of opposite-charge correlations, which is calculated in the jet frame for inclusive charged hadrons and the identified $π$, $K$, and $p$. The results show a clear narrowing of the balancing width with increasing jet charged multiplicity, indicating that particle production becomes more localized in momentum space in high-multiplicity jets.This trend resembles features attributed to collective expansion in heavy-ion collisions. The species dependence highlights sensitivity to the redistribution of strangeness and baryon number during string fragmentation and color reconnection. The new CR tune yields a little broader proton balance-function width in $Δφ^{*}$ than CP5, hinting at enhanced baryon-production dynamics, whereas meson widths differ only mildly. These comparisons suggest that multiparton interactions and color reconnection contribute to the observed trends, potentially generating collective like features inside jets, especially in high multiplicity jets, via nontrivial color dynamics alongside standard fragmentation. Taken together, the results establish identified hadron balance functions in high multiplicity jets as a sensitive probe of hadronization and provide new constraints for models of small system collectivity.

Figures (6)

• Figure 1: Two-dimensional balance functions from tune CP5 in pythia8 simulations for $\pi$, $K$, and $p$ in $pp$ collisions at $\sqrt{s} = 13.6$ TeV within individual jets. The top panel corresponds to $B(\Delta\eta^{*}, \Delta\phi^{*})$ in $20< N_\mathrm{ch}^{j} < 30$ intervals, and the bottom panel is for the $70< N_\mathrm{ch}^{j}< 80$ range. The left column (a, d) presents the $B(\Delta\eta^{*}, \Delta\phi^{*})$ for pions, the middle column (b, e) is for kaons, and the right column (c, f) is for protons. Both the trigger and associated particles are considered in $0.3 < j_\mathrm{T} < 3.0$ GeV.
• Figure 2: Two-dimensional balance functions from new CR in pythia8 simulations for $\pi$, $K$, and $p$ in $pp$ collisions at $\sqrt{s} = 13.6$ TeV within individual jets. The top panel corresponds to $B(\Delta\eta^{*}, \Delta\phi^{*})$ in $20< N_\mathrm{ch}^{j} < 30$ intervals, and the bottom panel is for the $70< N_\mathrm{ch}^{j} < 80$ range. The left column (a, d) presents the $B(\Delta\eta^{*}, \Delta\phi^{*})$ for pions, the middle column (b, e) is for kaons, and the right column (c, f) is for protons. Both the trigger and associated particles are considered in $0.3 < j_\mathrm{T} < 3.0$ GeV.
• Figure 3: One-dimensional $B$ projections along $\Delta\eta^{*}$ and $\Delta\phi^{*}$ from pythia8 model calculations in $pp$ collisions at $\sqrt{s} =$ 13.6 TeV for different particle species. $\Delta\eta^{*}$ projections are taken in $|\Delta\phi|^{*} \leq \pi/2$ and $\Delta\phi^{*}$ projections are taken in the $|\Delta\eta^{*}| \leq 1.0$ range. The top row (a, b) shows $B(\Delta\eta^{*})$ and $B(\Delta\phi^{*})$ for pions and charged hadrons, while the bottom row (c, d) presents the corresponding projections for kaons and protons. The results are shown for events with $20 < N_{\mathrm{ch}}^{j} < 30$, and both the trigger and associated particles are considered in $0.3 < j_\mathrm{T} < 3.0~\mathrm{GeV}$.
• Figure 4: The absolute (a, c) and the relative (b, d) width of $B$ projections along $\Delta\eta^{*}$ and $\Delta\phi^{*}$ from pythia8 model calculations for charged-hadron, $\pi, K, p$, respectively. Both the trigger and associated particles are considered in $0.3 < j_\mathrm{T} < 3.0~\mathrm{GeV}$.
• Figure 5: One-dimensional projections of the balance functions for CP5 and the new CR tune from the pythia8 model simulation of charged-hadrons in $pp$ collisions at $\sqrt{s} =$13.6 TeV. The left panel (a) shows the $B$ as a function of $\Delta\eta^{*}$, whereas the right panel (b) presents $B$ as a function of $\Delta\phi^{*}$. Both the trigger and associated particles are considered in $3.0 < j_\mathrm{T} < 6.0~\mathrm{GeV}$.