De-confinement in small systems: Clustering of color sources in high multiplicity pp collisions at s = 1.8TeV

It is shown that de-confinement can be achieved in high multiplicity nonjet [Formula: see text] collisions at [Formula: see text][Formula: see text]TeV Fermi National Accelerator Laboratory (FNAL- E735) experiment. Previously, the evidence for de-confinement was demonstrated by the constant freeze out energy density in high multiplicity events. In this paper, we use the same but analyze the transverse momentum spectrum in the framework of the clustering of color sources. This frame work naturally predicts the reduction in the charged particle multiplicity with respect to the value expected from the number of independent strings. The charged particle pseudorapidity densities in the range [Formula: see text] are considered. Results are presented for both thermodynamic and transport properties. The initial temperature and energy density are obtained from the data via the color reduction factor [Formula: see text] and the associated string density parameter [Formula: see text]. The Bjorken ideal fluid description of the [Formula: see text], when modified by the color reduction factor and the trace anomaly [Formula: see text] is in remarkable agreement with the lattice quantum chromo dynamics (LQCD) simulations. The energy density [Formula: see text] for [Formula: see text] is close to the value for 0–10% central events in Au+Au collisions at [Formula: see text][Formula: see text]GeV. The shear viscosity to entropy density ratio ([Formula: see text]) is [Formula: see text]0.2 at the transition temperature of 167[Formula: see text]MeV. The result for the trace anomaly [Formula: see text] is in excellent agreement with LQCD simulations. These results confirm our earlier observation that the de-confined state of matter was created in high multiplicity events in [Formula: see text] collisions at [Formula: see text][Formula: see text]TeV.

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