Measurement of R 2(Δη, Δφ) and P 2(Δη, Δφ) correlation functions in pp collisions at TeV with ALICE

Abstract

In high-energy collisions, the mechanism of particle production, diffusivity, and conservation of charge and momentum are all revealed by the two-particle normalised cumulants of particle number correlations (R 2) and transverse momentum, p T, correlations (P 2), which are measured as a function of relative pseudorapidity and relative azimuthal angle difference (Δη, Δφ). We measure these observables in pp collisions at TeV with transverse momentum (p T) range of 0.2 - 2.0 GeV/c, to complement the recent ALICE measurements in Pb–Pb collisions and for a better understanding of the jet contribution and nature of collectivity in small systems. The observed correlations on the near- and away-side are qualitatively similar, but differ quantitatively. Additionally, it is shown that the near-side peak of P 2 is much narrower than the near-side peak of R 2 for both charge-independent (CI) and charge-dependent (CD) combinations, similar to the recently published ALICE results in p—Pb and Pb—Pb collisions. These results not only establish a baseline for heavy-ion collisions but also help one to better understand signals that are compatible with the existence of collective effects in small systems because they are sensitive to the interplay between the underlying event and mini-jets in pp collisions.