Speaker
Description
The observation of a long-range, near-side, two-particle correlation (known as the ridge) has been over the past decade a key signature of the hydrodynamic evolution of the hot and strongly interacting matter produced in heavy-ion collisions. Indeed, the Quark-Gluon Plasma (QGP) appears to behave as a perfect fluid and latest results from LHC experiments in Pb-Pb collisions at 2.76 and 5.02 TeV show a nice agreement with hydrodynamic expectations, either for inclusive charged hadrons or identified particles. The observation of the ridge in high-multiplicity p-p and p-Pb collisions opened up new opportunities of exploring novel QCD dynamics in small colliding systems. While extensive studies of this long-range correlation phenomenon in p-Pb and p-p collisions have revealed its collective properties, the underlying mechanism that drives the collectivity in small colliding system remains unknown. A detailed investigation is needed to establish the cause of the observed collective behavior and to determine if, indeed, a QGP medium is being created or if another mechanism is responsible. Over the past year, the CMS experiment at the LHC has recorded a large amount of Pb-Pb, p-Pb and p-p collisions, opening new opportunities in the understanding of collective phenomena in high-multiplicity hadronic final state. Upon reviewing the experimental data from the CMS experiment and confronting them with theoretical models, a unified paradigm in describing the observed collectivity across all hadronic collision system is emerging. Potential future paths toward addressing key open questions, especially on collectivity in small colliding systems (p-A and p-p), will be discussed.
