Probing the microscopic origin of prompt and non-prompt $D^{0}$ production through event-shape engineering in proton-proton collisions at the LHC

TL;DR

This work investigates the microscopic origin of prompt and non-prompt $D^{0}$ production in proton–proton collisions at $\\sqrt{s}=13.6$ TeV using the PYTHIA8 generator, focusing on the roles of the hardest-scattering momentum transfer $\hat{p}_{\rm T}$, multi-parton interactions (MPI), and color reconnection (CR). By employing forward multiplicity via FT0M and the event-shape variable transverse spherocity $S_{0}$, the study connects inaccessible quantities like MPI to experimentally measurable proxies and dissects how event topology biases heavy-flavour production. Key findings show that self-normalised yields of both prompt and non-prompt $D^{0}$ increase with $\hat{p}_{\rm T}$ and $N_{\rm mpi}\rangle$, with non-prompt $D^{0}$ more sensitive to these drivers, indicating a dominant role of early hard scatterings in beauty production. The leading-$D^{0}$ momentum $p_{\rm T}^{D^{0}-\rm lead}$ tracks $\hat{p}_{\rm T}$ and MPI activity, while $S_{0}$ effectively separates jetty vs isotropic events; CR effects are modest, and $Q_{pp}$ exhibits topology-dependent spectral modifications. Overall, the work demonstrates the viability of event-shape engineering to interpret heavy-flavour production in small systems and provides guidance for experimental analyses of prompt vs non-prompt charm in high-multiplicity pp events.

Abstract

Heavy-flavour hadrons are produced in the early stages of ultra-relativistic collisions at the LHC via hard partonic interactions and experience the whole system evolution. The study of prompt and non-prompt $D^{0}$ mesons provides an independent avenue to test the theories of quantum chromodynamics and to investigate beauty hadron production. Moreover, the production of both prompt and non-prompt $D^{0}$ is influenced by microscopic processes such as multi-partonic interactions (MPI) and hadronisation through fragmentation. In this study, an attempt is made to understand the production of prompt and non-prompt $D^{0}$ mesons in proton-proton collisions at $\sqrt{s}=13.6$ TeV using the PYTHIA8 event generator, which offers a qualitative description of charm production. The role of the transverse momentum transfer in the hardest partonic scattering ($\hat{p}_{\rm T}$), MPI, and color reconnection is systematically explored. In addition, the charged particle production in different topological regions with respect to the leading $D^{0}$ meson is studied to assess the influence of the $D^{0}$ meson on the event topology and to examine the selection biases arising from the use of charged particle multiplicity as an event classifier.

Figures (11)

• Figure 1: Self-normalised yield of prompt and non-prompt $D^{0}$ measured at mid-rapidity compared with that of charged particles as a function of $\hat{p}_{\rm T}$ in pp collisions at $\sqrt{s}$ = 13.6 TeV using PYTHIA8.
• Figure 2: Self-normalised yield of prompt and non-prompt $D^{0}$ measured at mid-rapidity compared with that of charged particles as a function of $N_{\rm mpi}$ in pp collisions at $\sqrt{s}$ = 13.6 TeV using PYTHIA8.
• Figure 3: $\langle\hat{p}_{\rm T}\rangle$ (top) and $\langle N_{\rm mpi}\rangle$ (bottom) as function of $p_{\rm T}^{D^{0}-\rm lead}$ for prompt and non-prompt $D^{0}$ mesons in pp collisions at $\sqrt{s} = 13.6$ TeV measured at midrapidity ($|y|<0.5$) using PYTHIA8. The lower panel in both plots illustrates the CR off-to-CR on ratio.
• Figure 4: $\langle S_{0}\rangle$ versus $p_{\rm T}^{D^{0}-\rm lead}$ for MPI-on and MPI-off cases for prompt and non-prompt $D^{0}$ mesons in pp collisions at $\sqrt{s}~=~13.6$ TeV using PYTHIA8 for CR-on case.
• Figure 5: Self-normalised mid-rapidity charged particle multiplicity density versus $p_{\rm T}^{D^{0}-\rm lead}$ for toward, transverse and away regions defined with respect to the leading prompt and non-prompt $D^{0}$ for "MPI on" and "MPI off" cases in pp collisions at $\sqrt{s} = 13.6$ TeV using PYTHIA8.