Initial state fluctuations in collisions between light and heavy ions

TL;DR

This paper investigates how initial state fluctuations in small nucleus collisions affect the created matter's shape and size, highlighting the impact of nucleon substructure and multiplicity fluctuations on initial conditions.

Contribution

It provides a systematic analysis of initial state eccentricity coefficients considering nucleon substructure models and emphasizes the significance of multiplicity fluctuations in small nucleus collisions.

Findings

Large differences from Glauber model predictions.

Nucleon substructure significantly influences initial fireball shape.

Multiplicity fluctuations are crucial in small systems.

Abstract

In high energy collisions involving small nuclei (p+p or x+Au collisions where x=p, d, or $^3$He) the fluctuating size, shape and internal gluonic structure of the nucleon is shown to have a strong effect on the initial size and shape of the fireball of new matter created in the collision. A systematic study of the eccentricity coefficients describing this initial fireball state for several semi-realistic models of nucleon substructure and for several practically relevant collision systems involving small nuclei is presented. The key importance of multiplicity fluctuations in such systems is pointed out. Our results show large differences from expectations based on conventional Glauber model simulations of the initial state created in such collisions.