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-pr
oton 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.
Recent extensive data from the beam energy scan of the STAR collaboration at BNL-RHIC provide the basis for a detailed update for the universal behavior of the strangeness suppression factor gamma_s as function of the initial entropy density, as prop
osed in our recent paper [1]. [1] P. Castorina, S. Plumari and H. Satz, Int. J. Mod. Phys. E26 (2017) 1750081 (arXiv:1709.02706)
The interpretation of quark ($q$)- antiquark ($bar q$) pairs production and the sequential string breaking as tunneling through the event horizon of colour confinement leads to a thermal hadronic spectrum with a universal Unruh temperature, $T simeq
165$ Mev,related to the quark acceleration, $a$, by $T=a/2pi$. The resulting temperature depends on the quark mass and then on the content of the produced hadrons, causing a deviation from full equilibrium and hence a suppression of strange particle production in elementary collisions. In nucleus-nucleus collisions, where the quark density is much bigger, one has to introduce an average temperature (acceleration) which dilutes the quark mass effect and the strangeness suppression almost disappears.
Matter implies the existence of a large-scale connected cluster of a uniform nature. The appearance of such clusters as function of hadron density is specified by percolation theory. We can therefore formulate the freeze-out of interacting hadronic m
atter in terms of the percolation of hadronic clusters. The resulting freeze-out condition as function of temperature and baryo-chemical potential interpolates between resonance gas behaviour at low baryon density and repulsive nucleonic matter at low temperature, and it agrees well with data.
Using short distance QCD methods based on the operator product expansion, we calculate the $J/psi$ photoproduction cross section in terms of the gluon distribution function of the nucleon. Comparing the result with data, we show that experimental beh
aviour of the cross section correctly reflects the $x$-dependence of the gluon distribution obtained from deep inelastic scattering.
We extend a recent sum rule calculation for inelastic quarkonium-hadron interactions to realistic parton distribution functions; we also include finite target-mass corrections. Both modifications are shown to have no significant effect on the resulti
ng cross section behaviour but the performed analysis gives useful insights on the sum-rule approach in general.
