# Proton structure fluctuations: constraints from HERA and applications to p+A collisions

## TL;DR

This paper constrains proton structure fluctuations at small-x using HERA data and demonstrates their importance in modeling p+A collisions, showing compatibility with LHC measurements of momentum anisotropies.

## Contribution

It introduces constraints on proton structure fluctuations at small-x from HERA data and applies these to hydrodynamical simulations of p+A collisions.

## Key findings

- Large geometric fluctuations are necessary in the proton wave function.
- Hydrodynamical simulations with fluctuating proton structure match LHC anisotropy data.
- Proton structure fluctuations significantly impact p+A collision modeling.

## Abstract

We constrain proton structure fluctuations at small-$x$ by comparing with the HERA diffractive vector meson production data, and find that large geometric fluctuations in the proton wave function are needed. Hydrodynamical simulations of proton-nucleus collisions including the fluctuating proton structure are found to be compatible with the momentum anisotropies measured at the LHC.