A study of the charged-particle density (number density) in the transverse region of the dihadron correlations exploiting the existing pp and $\mathrm{p}\overline{\mathrm{p}}$ data from RHIC to LHC energies is reported. This region has contributions from the underlying event (UE) as well as from initial- and final-state radiation (ISR-FSR). Based on the data, a two-component model is built. This has the functional form $\propto s^{\alpha }+\beta \log (s)$, where the logarithmic ($\beta =0.140\pm 0.007$) and the power-law ($\alpha =0.270\pm 0.005$) terms describe the components more sensitive to the ISR-FSR and UE contributions, respectively. The model describes the data from RHIC to LHC energies; the extrapolation to higher energies indicates that at around $\sqrt{s}\approx 100\mathrm{TeV}$ the number density associated to UE will match that from ISR-FSR. Although this behavior is not predicted by pythia 8.244, the power-law behavior of the UE contribution is consistent with the energy dependence of the parameter that regulates multiparton interactions. Using simulations, KNO-like scaling properties of the multiplicity distributions in the regions sensitive to either UE or ISR-FSR are also discussed. The results presented here can be helpful to constrain QCD-inspired Monte Carlo models at the future circular collider energies, as well as to characterize the UE-based event classifiers which are currently used at the LHC.

• Received 20 August 2021
• Accepted 29 September 2021

DOI:https://doi.org/10.1103/PhysRevD.104.076019

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Published by the American Physical Society