Hot spots and gluon field fluctuations as causes of eccentricity in small systems

S Demirci,S Schlichting,T Lappi

doi:10.1103/physrevd.103.094025

Abstract

In this paper, the authors study the origin of eccentricity, or more generally, the azimuthal asymmetry in the initial conditions of small colliding systems, such as the proton nucleus system. Of the contending sources, namely color charge fluctuations and the geometric fluctuation of the so called hot spots in the proton, they conclude that the latter is by far the dominant cause of the asymmetry.

Highlights

Collective azimuthal correlations, commonly parametrized in terms of harmonic “flow” coefficients vn of produced particles, were a crucial experimental signal in the discovery of the strongly interacting quark-gluon plasma (QGP) in high-energy heavy ion collisions
We show that geometric fluctuations of hot spots inside the proton are the dominant source of eccentricity whereas color charge fluctuations only give a negligible correction
Since the lifetime of any such smaller collision system is significantly shorter than that of a heavy-ion collision, the emergence of such correlations was initially unexpected. This has led to an intense discussion [13] on whether the observed correlations in small collision system should be attributed to momentumspace correlations already present in the colliding projectiles [14,15,16,17,18,19,20,21], or whether they result from the final state response to the coordinate space geometry, either via hydrodynamical evolution [22,23,24] or by a simpler scattering mechanism [25,26,27,28,29,30,31]

Summary

Introduction

Collective azimuthal correlations, commonly parametrized in terms of harmonic “flow” coefficients vn of produced particles, were a crucial experimental signal in the discovery of the strongly interacting quark-gluon plasma (QGP) in high-energy heavy ion collisions. Since the lifetime of any such smaller collision system is significantly shorter than that of a heavy-ion collision, the emergence of such correlations was initially unexpected This has led to an intense discussion [13] on whether the observed correlations in small collision system should be attributed to momentumspace correlations already present in the colliding projectiles [14,15,16,17,18,19,20,21], or whether they result from the final state response to the coordinate space geometry, either via hydrodynamical evolution [22,23,24] or by a simpler scattering mechanism [25,26,27,28,29,30,31].

Objectives

Results

Conclusion