Topological production of charmonia with event-shape engineering in $pp$ collisions at $\sqrt{s} = 13$ TeV using PYTHIA8

TL;DR

This study investigates how event topology, probed with transverse spherocity $S_{0}$, shapes prompt and non-prompt $J/\psi$ production in $pp$ collisions at $\sqrt{s}=13$ TeV using PYTHIA8. By classifying events into jetty and isotropic topologies and analyzing dielectron and dimuon decay channels at mid- and forward rapidities, the work examines $p_{\rm T}$ spectra, the non-prompt fraction $f_{\rm B}$, and a partonic modification factor $Q_{pp}$ to quantify topology-driven modifications. The results show that MPI and color reconnection can harden prompt $J/\psi$ spectra in isotropic events and boost non-prompt production at moderate $p_{\rm T}$, while forward rapidity exhibits diminished MPI influence and reduced biases, with $f_{\rm B}$ increasing with $p_{\rm T}$ and $\langle p_{\rm T} \rangle$ rising with multiplicity. These findings demonstrate the value of event-shape engineering for disentangling heavy-flavor production mechanisms in small systems and provide a framework to interpret Run 3 pp data and jet-associated quarkonium production.

Abstract

The production of heavy quarks (charm and beauty) in high-energy hadronic and nuclear collisions provides an excellent testing ground for the theory of strong interaction and validates models based on quantum chromodynamics. In this work, prompt and nonprompt production of $\rm{J/}ψ$ in $pp$ collisions at $\sqrt{s}=13$ TeV are studied as a function of transverse spherocity using PYTHIA8. $\rm{J/}ψ$ is reconstructed via its electromagnetic decay to dielectrons and dimuons, in mid- and forward-rapidity, respectively. Transverse spherocity, an event shape observable, is used to distinguish hard QCD events from the softer, isotropic ones. In PYTHIA8, the production of $\rm{J/}ψ$ can be influenced by the average number of multiple parton interactions ($\langle N_{\rm mpi} \rangle$), owing to the underlying events (UE), which have a dominant contribution to particle production at lower transverse momentum. Since transverse spherocity is correlated to $\langle N_{\rm mpi} \rangle$, this can serve as an experimentally available tool for event selection to study the underlying QCD processes influencing the prompt and nonprompt $\rm{J/}ψ$ production. This study reveals the correlation between heavy-flavor production dynamics and topological event selection in $pp$ collisions using PYTHIA8, whose relevance awaits experimental validation.

Figures (8)

• Figure 1: (Color online) Event-normalized transverse momentum ($p_{\rm T}$) spectra of prompt and non-prompt $\rm{J}/\psi$ in $S_{0}$-integrated, jetty and isotropic events from $pp$ collisions at $\sqrt{s}$ = 13 TeV using PYTHIA8, for dielectron (left) and dimuon (right) production channels at $|y| < 0.9$ and $2.5 < y < 4$ rapidity ranges respectively for (0--100%) V0M class. The ratio of $p_{\rm T}$ spectra of the jetty and isotropic to $S_{0}$-integrated events is shown in the bottom panel.
• Figure 2: (Color online) $Q_{\rm pp}$ as a function of $p_{\rm T}$ for prompt and non-prompt $\rm{J}/\psi$ in mid (left) and forward (right) rapidities for jetty and isotropic events in $pp$ collisions at $\sqrt{s}$ = 13 TeV using PYTHIA8.
• Figure 3: (Color online) The fraction of non-prompt $\rm{J}/\psi$ produced as a function of $p_{\rm T}$ in midrapidity (left) and forward rapidity (right) for $S_{0}$-integrated, jetty and isotropic events from $pp$ collisions at $\sqrt{s}$ = 13 TeV using PYTHIA8
• Figure 4: (Color online) Mean transverse momentum ($\langle p_{\rm T} \rangle$) as a function of midrapidity charged particle multiplicity density for prompt and non-prompt $\rm{J}/\psi$ in mid (left) and forward (right) rapidity regions for $S_{0}$-integrated, jetty and isotropic events for $pp$ collisions at $\sqrt{s}$ = 13 TeV using PYTHIA8
• Figure 5: (Color online) Normalized $p_{\rm T}$-integrated prompt and non-prompt $\rm{J}/\psi$ yield as a function of normalized charged particle multiplicity density at midrapidity region ($|\eta| < 0.5$) with V0 multiplicity selection, for $S_{0}$-integrated, jetty and isotropic events from $pp$ collisions at $\sqrt{s}$ = 13 TeV using PYTHIA8, for dielectron (left) and dimuon (right) production channels at $|y| < 0.9$ and $2.5 < y < 4$ rapidity ranges respectively. The dashed black line guides $(dN_{\rm{J}/\psi}/dy)/(\langle dN_{\rm{J}/\psi}/dy \rangle)$ = $(dN_{\rm ch}/d\eta)/(\langle dN_{\rm ch}/d\eta \rangle)$.