Glauber modeling of high-energy nuclear collisions at sub-nucleon level

TL;DR

This paper extends the Glauber model to include sub-nucleon degrees of freedom, enabling more detailed initial state characterization in high-energy nuclear collisions, with results indicating particle production scales with 3 to 5 constituents.

Contribution

The paper introduces a novel extension of the Glauber model that incorporates multiple sub-nucleon constituents, enhancing the understanding of initial collision states.

Findings

Particle production scales with 3-5 sub-nucleon degrees of freedom.

Initial state properties vary with sub-nucleon distribution assumptions.

Source codes for the extended model are publicly available.

Abstract

Glauber models based on nucleon--nucleon interactions are commonly used to characterize the initial state in high-energy nuclear collisions, and the dependence of its properties on impact parameter or number of participating nucleons. In this paper, an extension to the Glauber model is presented, which accounts for an arbitrary number of effective sub-nucleon degrees of freedom, or active constituents, in the nucleons. Properties of the initial state, such as the number of constituent participants and collisions, as well as eccentricity and triangularity, are calculated and systematically compared for different assumptions of how to distribute the sub-nuclear degrees of freedom and for various collision systems. It is demonstrated that at high collision energy the number of produced particles scales with an average number of sub-nucleon degrees of freedom of between $3$ and $5$. The source codes for the constituent Monte Carlo Glauber extension, as well as for the calculation of the overlap area and participant density in a standard Glauber model, are made publicly available.