Initial energy density of $\sqrt{s}=$ 7 and 8 TeV p+p collisions at the LHC

TL;DR

This paper uses relativistic hydrodynamics solutions to estimate the initial energy density in high-energy proton-proton collisions at the LHC, finding it comparable to the critical density for quark-gluon plasma formation.

Contribution

It introduces an advanced hydrodynamic method to estimate initial energy density in pp collisions, linking it to the creation of a perfect fluid state.

Findings

Initial energy density in 7 and 8 TeV pp collisions is on the order of the QCD critical density.

High multiplicity pp collisions can reach energy densities sufficient for non-hadronic fluid formation.

Estimated initial temperature approaches the QCD critical and Hagedorn temperatures.

Abstract

Results from the RHIC and LHC experiments show, that in relativistic heavy ion collisions, a new state of matter, a strongly interacting perfect fluid is created. Accelerating, exact and explicit solutions of relativistic hydrodynamics allow for a simple and natural description of this medium. A finite rapidity distribution arises from these solutions, leading to an advanced estimate of the initial energy density of high energy collisions. These solutions can be utilized to describe various aspects of proton-proton collisions, as originally suggested by Landau. We show that an advanced estimate based on hydrodynamics yields an initial energy density in $\sqrt{s}=7$ and 8 TeV p+p collisions at LHC on the same order as the critical energy density from lattice QCD, and a corresponding initial temperature around the critical temperature from QCD and the Hagedorn temperature. The multiplicity dependence of the estimated initial energy density suggests that in high multiplicity pp collisions at the LHC, there is large enough initial energy density to create a non-hadronic perfect fluid.