Strangeness enhancement and flow-like effects in $e^+ e^-$ annihilation at high parton density

TL;DR

This paper investigates why strangeness enhancement and flow-like effects, common in heavy ion collisions, are absent in electron-positron annihilation, attributing it to lower parton densities.

Contribution

It demonstrates that the low parton density in $e^+ e^-$ annihilation explains the lack of collective phenomena observed in other high-energy collisions.

Findings

Parton density in $e^+ e^-$ is too low for collective effects.

No observed strangeness enhancement in $e^+ e^-$ data.

Event-by-event multiplicity analysis supports low-density explanation.

Abstract

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 ("small systems") scatterings. Indeed, 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. On the other hand, $e^+ e^-$ annihilation data at LEP and lower energies indicate that there is no strangeness enhancement and no flow-like effect. We show that the parton density in the transverse plane generated in $e^+ e^-$ annihilation at the available energy is too low to expect such effects. The event-by-event multiplicity where strangeness suppression and flow-like phenomenon could show up in $e^+ e^-$ is evaluated.