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

It is shown that de-confinement can be achieved in high multiplicity nonjet p¯p collisions at √s =1.8 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 7.0 ≤ 〈dN_c/dη〉 ≤ 26.0 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 F(ξ) and the associated string density parameter ξ. The Bjorken ideal fluid description of the QGP, when modified by the color reduction factor and the trace anomaly Δ is in remarkable agreement with the lattice quantum chromo dynamics (LQCD) simulations. The energy density (ε/T⁴) ∼ 11.5 or 〈dN_c/dη〉 25.0 is close to the value for 0–10% central events in Au + Au collisions at √s_NN = 200 GeV. The shear viscosity to entropy density ratio (η/s) is ∼ 0.2 at the transition temperature of 167 MeV. The result for the trace anomaly Δ 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 p¯p collisions at √s = 1.8 TeV. (author)