# How cross section fluctuations affect multiplicity and geometry in pA collisions

## TL;DR

This paper introduces a new Monte Carlo Glauber model for pA collisions using cross sections from the KMR model, showing improved descriptions of particle multiplicity and spatial anisotropy.

## Contribution

A new Monte Carlo Glauber model for pA collisions using KMR cross sections is introduced, offering better multiplicity and geometry predictions.

## Key findings

- KMR/SHRiMPS cross sections provide good descriptions of multiplicity distributions in pA collisions.
- These cross sections increase anisotropy in the spatial distribution of wounded nucleons.
- The model generalizes straightforwardly to A+A collisions.

## Abstract

In this paper, a new Monte Carlo Glauber model is developed for pA collisions. It uses the hadronic cross sections calculated within the KMR model as implemented in the SHRiMPS minimum bias module of the SHERPA event generator. These cross sections are obtained as functions of impact parameter and, therefore, are ready for use in a Glauber model without additional assumptions regarding their impact parameter dependence. We compare the results obtained with those from a Black Disk model and from another model with colour fluctuations. It is shown that the KMR/SHRiMPS cross sections may present very good descriptions of the multiplicity distributions in pA collisions given that they show a long tail in the distribution of wounded nucleons. Moreover, it is shown that they also increase the anisotropy in the spatial distribution of wounded nucleons, which can be important in the description of the initial states of pA collisions. The generalization to A+A collisions is straightforward.