Energy dependence of underlying-event observables from RHIC to LHC energies

A study of the charged-particle density (number density) in the transverse region of the dihadron correlations exploiting the existing pp and pp 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 proportional to s(alpha) + beta log(s), where the logarithmic (beta = 0.140 +/- 0.007) and the power-law (alpha = 0.270 +/- 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 root s approximate to 100 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.

Automated summary

This study reports on the charged-particle density in the transverse region of dihadron correlations, utilizing existing data from pp collisions at RHIC to LHC energies. A two-component model is built, with different terms sensitive to ISR-FSR and UE contributions. The results provide insight into constraining Monte Carlo models and characterizing event classifiers at future collider energies.