Abstract: The Quark-Gluon Plasma (QGP) is a phase of strongly interacting matter where the relevant degrees of freedom are deconfined partons.
Ultra-relativistic heavy-ion (A-A) collisions provide the optimum conditions for creating the QGP in the laboratory: the necessary energy densities are estimated to be comparable to those of the early Universe a couple of microseconds after the big bang.
Large collaborations of physicists at CERN and RHIC have been focusing on the characterisation of the QGP for several decades and managed to extract many properties of the QGP to a very high precision level.
When studying flavour production within the QGP, proton-proton (pp) collisions are generally used as a baseline where no plasma is expected to be created. For instance, a historical signature of the QGP relies on the relative enhancement of strangeness production in A-A collisions compared to pp. With the advent of pp collisions at several TeV provided by the Large Hadron Collider, it is legitimate to reassess the validity of using such collisions for baseline measurements.
After a reminder of the strangeness enhancement initially conceived as a direct consequence of the deconfined medium in A-A, recent measurements obtained with ALICE in pp as a function of charged particle multiplicity (Nature Physics 13, 535–539, 2017) will be presented. We will then discuss possible interpretations and further directions in the light of these results.