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

Two-particle pseudorapidity correlations are measured in $\sqrt{s_{\rm{NN}}}$=2.76 TeV Pb+Pb, $\sqrt{s_{\rm{NN}}}$=5.02 TeV $p$+Pb and $\sqrt{s}$ =13 TeV $pp$ collisions~\cite{ATLAS}. 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 $1+\left\langle a_1^2\right\rangle\eta_1\eta_2$ in all collision systems over the full multiplicity range. The values of $\left\langle a_1^2\right\rangle$ are consistent between the opposite-charge and same-charge pairs, and are similar for the three collision systems at similar multiplicity. The values of $\left\langle a_1^2\right\rangle$ and the magnitude of the SRC both follow a power-law dependence on the event multiplicity.