Measurement of $R_{2}(\Delta\eta, \Delta\varphi)$ and $P_{2}(\Delta\eta, \Delta\varphi)$ correlation functions in pp collisions at $\sqrt{\textit{s}}$ = 13 TeV using ALICE data

Abstract

Two-particle normalized cumulants of particle number correlations ($R_{2}$) and transverse momentum correlations ($P_{2}$), measured as a function of relative pseudorapidity and azimuthal angle difference $(\Delta\eta, \Delta\varphi)$, provide key information about particle production mechanisms, diffusivity, and conservation of charge and momentum in high-energy collisions. To complement the recent ALICE measurements in Pb--Pb collisions, as well as for better understanding of the jet contribution and nature of collectivity in small systems, these observables are measured in pp collisions at $\sqrt{\textit{s}}$ = 13 TeV with similar transverse momentum range, 0.2 $\leq$ $\textit{p}_{\rm T}$ $\leq$ 2.0 $\rm{GeV}/\textit{c}$. The $R_{2}$ and $P_{2}$ results on the near- and away-side are qualitatively similar, but differ quantitatively. A much narrower near-side peak is observed for $P_{2}$ compared to $R_{2}$ for both charge-independent and charge-dependent combinations, as in the recently published ALICE results for p--Pb and Pb--Pb collisions. Since these results are sensitive to the interplay between the underlying event and mini-jets in pp collisions, they not only establish a baseline for heavy-ion collisions, but also allow a better understanding of signals that are compatible with the presence of collective effects in small systems.