Long-range angular correlations in soft and hard pPb collisions at a center-of-mass energy of 5.02 TeV measured with ALICE

Previous studies of two-particle correlation in proton-lead (pPb) collisions at $\sqrt{s}$ = 5.02TeV revealed a so-called $double$ $ridge$ structure similar to the one observed in lead-lead (PbPb) collisions. This structure features two distinct ridges extending over the entire $\Delta$$\eta$ range (long-range correlations) at $\Delta\phi$ $\approx$ 0 (near-side) and $\Delta\phi$ $\approx$ $\pi$ (away-side). A model based on hydrodynamical expansion is capable of modeling this effect but requires that a spatially extended strongly-interacting medium is created. While such an assumption is reasonable for PbPb collisions, it is not justifiable in pPb collisions creating the need of an alternative description of the effect in the latter system. The following thesis presents the aforementioned hydrodynamical model and two proposed alternatives: The Color Glass Condensate and Color Reconnection (CR). A falsification of the models is undertaken by studying the dependence of the two-particle correlations on the $hardness$ of the underlying events. A multiplicity dependent bias towards di-jets in low multiplicity events was introduced by hardening the event sample, leaving the long-range near-side area of the double ridge for the extraction of an unbiased $ridge$ $yield$. No dependence of the ridge yield on the hardness of the event was found within the margin of uncertainty. This observation disfavors CR but detailed theoretical studies of CR in pPb and the study of a so-called $soft$ event sample are needed to rule out this model conclusively.