Forward-backward multiplicity correlations with the observable Σ at LHC energies

This talk presents the first-ever ALICE results on forward–backward multiplicity correlations, studied with the strongly intensive quantity Σ for charged particles produced in Xe–Xe collisions at √sNN = 5.44 TeV and Pb–Pb collisions at √sNN = 2.76 and 5.02 TeV. These new data are compared with proton-proton results at √s = 13 TeV. Σ appears independent of the centrality selection method and of system volume fluctuations,  but shows a clear dependence on system size and collision centrality. None of the commonly used microscopic models (HIJING, AMPT, EPOS-LHC) reproduces the experimental data. In contrast, the Kraków Wounded Nucleon and Wounded Quark Models describe the data very well and provide a natural interpretation for the observed trends. What is more, Σ enables a new method for extracting the fragmentation function of Wounded Constituents—for the first time applicable in symmetric nucleus–nucleus collisions. Although within the Wounded Constituent picture, Σ is no longer a strongly intensive quantity, it remains a robust and informative measure of forward–backward correlations. The connections between this quantity and other commonly used correlation observables, as well as its advantages in the general context of interpretation of particle correlation and fluctuation data will also be addressed in the talk.