The production of hadrons containing one or more strange quarks has been measured in heavy-ion collisions for more than 30 years to investigate the formation of the deconfined medium known as Quark Gluon Plasma (QGP) and its thermal properties. Measurements in systems such as proton-nucleus (p-A) or proton-proton (pp) collisions have been traditionally used as a baseline, until the observation of strangeness enhancement in high-multiplicity pp collisions by the ALICE experiment at the CERN Large Hadron Collider has opened new perspectives.
After a short historical excursus through the milestones in the study of strangeness production as a QGP signature, the latest measurements with ALICE will be presented. Results include energy- and multiplicity-dependence of strangeness production from small to large systems, discussed in comparison with model predictions.
As the observed strangeness enhancement adds to a set of previous measurements showing that pp collisions exhibit characteristic features known from high-energy heavy-ion collisions, the questions are open: is it strangeness enhancement not a unique feature of QGP formation? Can high-multiplicity pp collisions provide information on the onset of deconfinement?