Probing non-perturbative QCD aspects on particle production in pp collisions with forward-backward correlations using \texttt{PYTHIA8}

TL;DR

This study uses PYTHIA8 simulations to analyze forward-backward correlations in proton-proton collisions at LHC energies, revealing the significant roles of non-perturbative QCD effects like color reconnection and QCD radiation in particle production.

Contribution

It provides a systematic analysis of how non-perturbative QCD effects influence forward-backward correlations, with detailed insights into the roles of color reconnection and QCD radiation.

Findings

MPI-based CR and QCD Color Rope improve data agreement

ISR/FSR critically affect correlation observables

CR strength influences correlation magnitudes differently for extensive and intensive measures

Abstract

We employ PYTHIA8 simulations to study forward-backward (FB) correlations in pp collisions at LHC energies, probing non-perturbative QCD dynamics via color reconnection (CR) and QCD radiation (ISR/FSR). Using \texttt{PYTHIA8} (v8.311) under ALICE/ATLAS kinematics, we analyze: extensive: FB multiplicity ($b_{\rm corr}^{\rm mult}$) and summed $p_{\rm T}$ ($b_{\rm corr}^{\sum p_{\rm T}}$) correlations; intensive: FB mean $p_{\rm T}$ ($b_{\rm corr}^{\overline p_{\rm T}}$) correlations; and \textit{strongly intensive:} $\Sigma_{\rm N_F N_B}$ quantity in symmetric pseudorapidity intervals, validated against available experimental data. Systematic studies of $b_{\rm corr}^{\rm mult}$ as functions of $\eta_{\rm gap}$, $\eta_{\rm sep}$, and $\eta$-$\varphi$ sectors show MPI-based CR (ranges 3.6, 5.4) and QCD Color Rope significantly improve agreement with data. ISR/FSR critically influence $b_{\rm corr}^{\rm mult}$ and $b_{\rm corr}^{\sum p_{\rm T}}$, with ISR dominant than FSR. Disabling ISR/FSR fails to replicate $\eta_{\rm gap}$-dependent trends. Further, $b_{\rm corr}^{\sum p_{\rm T}}$ shows minimal CR-range sensitivity but the correlation strength increases when CR is disabled. Intensive quantity, $b_{\rm corr}^{\overline p_{\rm T}}$, exhibit the opposite behavior to extensive observables i.e. the magnitude of $b_{\rm corr}^{\overline p_{\rm T}}$ increases with the increase of CR strength, highlighting the distinct influence of CR on intensive versus extensive observables. Its azimuthal dependence indicates that parton showers drive short-range correlations. The analysis of the strongly intensive quantity as a function of pseudorapidity gap indicates that FSR plays a dominant role at larger gaps, in contrast to the behavior observed in FB multiplicity correlations.