Collective flow in high-multiplicity proton-proton collisions

TL;DR

This paper provides evidence of strong radial flow in high-multiplicity proton-proton collisions at 7 TeV, demonstrating the applicability and limitations of hydrodynamic models in such small systems.

Contribution

It shows that hydrodynamic descriptions can fit high-multiplicity pp collision data, revealing collective behavior and constraining initial fireball size, while highlighting their limitations at lower multiplicities.

Findings

Hydrodynamic model fits high-multiplicity pp data

Initial fireball size estimated around 1 fm

Hydrodynamics fails at lower multiplicities

Abstract

We present an evidence of strong radial flow in high-multiplicity pp collisions. We analyze the CMS data on the inclusive spectra of the charged pions, kaons and protons in the LHC $\sqrt{s}=7$ TeV collisions. For $<N_{\mathrm{tracks}} >\gtrsim 75$ we demonstrate the consistency of the hydrodynamic description with the (idealized) Gubser's flow. Using a one parameter fit of the model to experimental data, we obtain the initial fireball size to be of the order of 1 fm. At smaller multiplicities, the fit cannot be performed which shows a limitation of the hydrodynamic approach and provides us with falsifiability of our theory.