# Flow in small and large quark-gluon plasma droplets: the role of nucleon substructure

## TL;DR

This paper investigates how nucleon substructure influences bulk observables in proton-lead collisions at the LHC, using Bayesian methods to calibrate a model with Gaussian partons within nucleons.

## Contribution

It introduces a nucleon substructure model with variable partons into the initial condition framework and calibrates it using Bayesian analysis to better understand small system hydrodynamics.

## Key findings

- Partonic substructure affects particle correlations in small systems.
- Bayesian calibration constrains nucleon substructure parameters.
- Model viability for small system hydrodynamics is supported.

## Abstract

We study the effects of nucleon substructure on bulk observables in proton-lead collisions at the LHC using Bayesian methodology. Substructure is added to the TRENTO parametric initial condition model using Gaussian nucleons with a variable number of Gaussian partons. We vary the number and width of these partons while recovering the desired inelastic proton-proton cross section and ensemble averaged proton density. We then run the model through a large number of minimum bias hydrodynamic simulations and measure the response of final particle production and azimuthal particle correlations to initial state properties. Once these response functions are determined, we calibrate free parameters of the model using established Bayesian methodology. We comment on the implied viability of the partonic model for describing hydrodynamic behavior in small systems.