Eccentricity fluctuations make flow measurable in high multiplicity p-p collisions

TL;DR

This paper demonstrates that fluctuations in high-multiplicity proton-proton collisions at the LHC can produce measurable elliptic flow signals, previously thought exclusive to heavy ion collisions, under certain conditions.

Contribution

It identifies conditions under which elliptic flow can be measured in high-multiplicity p-p collisions, expanding the applicability of flow analysis techniques.

Findings

Fluctuations can induce sizable spatial eccentricity in central p-p collisions.

Elliptic flow signals become measurable in high-multiplicity p-p collisions at the LHC.

Standard analysis techniques are sufficient to detect flow in these conditions.

Abstract

Elliptic flow is a hallmark of collectivity in hadronic collisions. Its measurement relies on analysis techniques which require high event multiplicity and could be applied so far to heavy ion collisions only. Here, we delineate the conditions under which elliptic flow becomes measurable in the samples of high-multiplicity ($dN_{\rm ch}/dy \geq 50$) p-p collisions, which will soon be collected at the LHC. We observe that fluctuations in the p-p interaction region can result in a sizable spatial eccentricity even for the most central p-p collisions. Under relatively mild assumptions on the nature of such fluctuations and on the eccentricity scaling of elliptic flow, we find that the resulting elliptic flow signal in high-multiplicity p-p collisions at the LHC becomes measurable with standard techniques.