Eccentricity and elliptic flow in proton-proton collisions from parton evolution

Abstract

It has been argued that high-multiplicity proton-proton collisions at the LHC may exhibit collective phenomena usually studied in the context of heavy-ion collisions, such as elliptic flow. We study this issue using DIPSY - a Monte Carlo event generator based on the QCD dipole model. We calculate the eccentricity of the transverse area defined by the spatial distribution of produced gluons. The resulting elliptic flow is estimated to be about 6%, comparable to the value in nucleus-nucleus collisions at RHIC and the LHC. Experimentally, elliptic flow is inferred from the azimuthal correlation between hadrons, which receives contributions from collective flow, and from various other effects referred to as "nonflow". We discuss how to identify in experiments the signal of flow in the presence of large nonflow effects.

v2: Four-particle correlation added, improved discussions on the signatures of flow. v3: Improved treatment of fluctuations in the flow analysis. v4: Minor changes for journal submission

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• The centrality dependence of elliptic flow, the hydrodynamic limit, and the viscosity of hot QCD
• Effect of flow fluctuations and nonflow on elliptic flow methods
• Eccentricity fluctuations and elliptic flow at RHIC
• Elastic and quasi-elastic $pp$ and ${\gamma }^{\star }p$ scattering in the Dipole Model
• Correlation of small-x gluons in impact parameter space
• Quantitative study of the transverse correlation of soft gluons in high energy QCD

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