# Hard diffraction in photoproduction with Pythia 8

## TL;DR

This paper introduces a new Pythia 8-based model for simulating hard diffractive events in photoproduction, extending previous models to include various beam types and explaining observed factorization breaking at HERA.

## Contribution

The paper develops a comprehensive framework for modeling hard diffraction in photoproduction within Pythia 8, incorporating multiple existing ideas and extending previous models to new beam types.

## Key findings

- Good agreement with HERA data on diffractive dijet events
- Model applicable to ultraperipheral collisions at LHC
- Provides predictions for pp and pPb collisions

## Abstract

We present a new framework for modeling hard diffractive events in photoproduction, implemented in the general purpose event generator Pythia 8. The model is an extension of the model for hard diffraction with dynamical gap survival in pp and ppbar collisions proposed in 2015, now also allowing for other beam types. It thus relies on several existing ideas: the Ingelman-Schlein approach, the framework for multiparton interactions and the recently developed framework for photoproduction in gamma p, gamma gamma, ep and $e^+e^-$ collisions. The model proposes an explanation for the observed factorization breaking in photoproduced diffractive dijet events at HERA, showing an overall good agreement with data. The model is also applicable to ultraperipheral collisions with pp and pPb beams, and predictions are made for such events at the LHC.