Correlations in Particle Production in Nuclear Collisions at LHC Energies

New data on forward-backward charged particle correlations and multiplicity uctuations in Pb+Pb collisions at p sNN = 2.76 TeV measured by the ALICE detector at CERN are presented. The analysis focuses on the dependence of (a) the correlation coecient bcorr, (b) the intensive quantity ! and (c) the strongly-intensive quantity as a function of (1) the pseudorapidity gap (2) the centrality of the collision and (3) the width of the centrality bin. The considered observables are studied for Pb+Pb data with two dierent centrality estimators. The centrality selection methods are based on charged particle multiplicity measurement by the ALICE VZERO detector and on determination of energy carried by spectator systems by the Zero Degree Calorimeter. A strong dependence of the measured magnitude of forward-backward correlation (bcorr), and of the size of multiplicity uctuations (!), is observed as a function of the ap- plied centrality estimator and as a function of the size of centrality window. A dominant eect on the correlation strength and multiplicity uctuations from geometrical uctu- ations is apparent for wide centrality class windows. This eect decreases signicantly with narrowing the size of centrality class bin. The presented work veries that the observable exhibits the properties of strongly intensive quantity in terms of Independent Source Model for Pb+Pb collisions at ALICE energies. Thus the usage of the strongly intensive quantity makes measurement inde- pendent on \trivial" eects like the number of nucleons participating in the collision and its uctuations. The results on centrality selected Pb+Pb collisions (from peripheral to central) are compared to elementary p+p collisions at the same collision energy, showing the role of the system size w.r.t. short-range and long-range correlations present in the process. A comparison of the obtained results to Monte Carlo simulations shows that the detailed nature of the interplay between short-range and long range correlations requires a further eort in phenomenological understanding.