Strangeness enhancement and collective flow are considered signatures of the quark gluon plasma formation. These phenomena have been detected not only in relativistic heavy ion collisions but also in high energy, high multiplicity events of proton-proton and proton-nucleus (“smallsystems”) scatterings.
A universal behavior emerges by considering the parton density in the
transverse plane as the dynamical quantity to specify the initial condition of the collisions, which in e + e − annihilation at the available energies is too low to expect collective effects.