Forward-backward multiplicity correlations in pp, pPb and Pb+Pb collisions with the ATLAS detector

Two-particle pseudorapidity correlations are measured in 2.76 TeV Pb+Pb, 5.02 TeV pPb and 13 TeV pp collisions. Correlation function is measured using charged particles in the pseudorapidity range $|\eta|<2.4$ with transverse momentum $p_T>0.2$ GeV, and it is measured as a function of event multiplicity, defined by number of charged particles with $|\eta|<2.5$ and $p_T>0.4$ GeV. The correlation function is decomposed into a short-range component (SRC) and a long-range component (LRC). The SRC differs significantly between the opposite-charge pairs and same-charge pairs, and between the three collision systems at similar multiplicity. The LRC is described approximately by $1+\langle a_1^2\rangle\eta_1\eta_2$ in all collision systems over the full multiplicity range. The values of $\langle a_1^2\rangle$ are consistent between the opposite-charge and same-charge pairs, and are similar for the three collision systems at similar multiplicity. The values of $\langle a_1^2\rangle$ and the magnitude of the SRC both follow a power-law dependence on the event multiplicity.