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

TL;DR

This paper investigates the potential for collective phenomena like elliptic flow in high-multiplicity proton-proton collisions at the LHC using a QCD dipole model-based Monte Carlo generator, estimating a flow comparable to heavy-ion collisions.

Contribution

It introduces a method to calculate eccentricity and elliptic flow in proton-proton collisions using the DIPSY Monte Carlo generator, highlighting the possibility of observing collective effects.

Findings

Estimated elliptic flow of about 6% in proton-proton collisions.

Eccentricity of the transverse area defined by gluon distribution.

Discussion on experimental identification of flow signals amidst nonflow effects.

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.