Measurement of forward-backward multiplicity correlations in lead-lead, proton-lead, and proton-proton collisions with the ATLAS detector

Abstract

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 at the LHC, with total integrated luminosities of approximately 7 \(\mu\mathrm{b}^{-1}\), 28 \(\mathrm{nb}^{-1}\), and 65 \(\mathrm{nb}^{-1}\), respectively. The correlation function \(C_{\rm N}(\eta_1,\eta_2)\) is measured as a function of event multiplicity using charged particles in the pseudorapidity range \(|\eta|<2.4\), The correlation function contains a significant short-range component, which is estimated and subtracted. After removal of the short-range component, the shape of the correlation function 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 \(\sqrt{\langle{a_1^2}\rangle}\) are consistent between the opposite-charge pairs and same-charge pairs, and for the three collision systems at similar multiplicity. The values of \(\sqrt{\langle{a_1^2}\rangle}\) and the magnitude of the short-range component both follow a power-law dependence on the event multiplicity. The \(\eta\) distribution of the short-range component, after symmetrizing the proton and lead directions in \(p\)+Pb collisions, is found to be smaller than that in \(pp\) collisions with comparable multiplicity.