Testing Hydrodynamic Descriptions of of p+p Collisions at \sqrt{s}=7 TeV

TL;DR

This paper investigates whether hydrodynamic models can accurately describe particle behavior in proton-proton collisions at 7 TeV, finding that hydrodynamics can reliably predict certain observables with appropriate parameters.

Contribution

It demonstrates the applicability of hydrodynamic modeling to small p+p collision systems and explores the limits of hydrodynamics in such contexts.

Findings

Hydrodynamics accurately predicts particle spectra.

Hydrodynamics reproduces elliptic flow coefficient $v_2$.

Small bulk viscosity improves model agreement.

Abstract

In high energy collisions of heavy-ions, experimental findings of collective flow are customarily associated with the presence of a thermalized medium expanding according to the laws of hydrodynamics. Recently, the ATLAS, CMS and ALICE experiments found signals of the same type and magnitude in ultrarelativistic proton-proton collisions. In this study, the state-of-the-art hydrodynamic model SONIC is used to simulate the systems created in p+p collisions. By varying the size of the second-order transport coefficients, the range of applicability of hydrodynamics itself to the systems created in p+p collisions is quantified. It is found that hydrodynamics can give quantitatively reliable results for the particle spectra and the elliptic momentum anisotropy coefficient $v_2$. Using a simple geometric model of the proton based on the elastic form factor leads to results of similar type and magnitude to those found in experiment when allowing for a small bulk viscosity coefficient.