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Diffraction in Pythia

Sparsh Navin

TL;DR

Diffraction in PYTHIA develops a Pomeron-based diffraction model integrated with standard event-generation components, covering both soft and hard regimes. It documents the evolution from PYTHIA 6's Schuler–Sjöstrand framework to PYTHIA 8.130 with multiple Pomeron flux parameterizations and distinct low- and high-mass diffraction treatments using diffractive PDFs. The study compares PYTHIA with PHOJET, showing that incorporating hard diffraction improves p_T and multiplicity tails, aiding agreement with alternative models. It also highlights key uncertainties in Pomeron flux and cross-section, and outlines future enhancements, including central diffraction and extensive data validation.

Abstract

The PYTHIA program can be used to generate high-energy-physics 'events' with sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide a representation, as accurate as possible, of event properties in a wide range of reactions. One such reaction, that is not well understood is Diffraction. Among the several alternative approaches that have been proposed, in PYTHIA, we follow a fairly conventional Pomeron based one, but fully integrated to use the standard PYTHIA machinery for multiple interactions, parton showers and hadronization. This note reports the development in PYTHIA in the way diffraction is modeled without providing specific details for usage. Results are compared with an alternative event generator called PHOJET. The code and further information may be found on the Pythia web page: http://home.thep.lu.se/~torbjorn/Pythia.html.

Diffraction in Pythia

TL;DR

Diffraction in PYTHIA develops a Pomeron-based diffraction model integrated with standard event-generation components, covering both soft and hard regimes. It documents the evolution from PYTHIA 6's Schuler–Sjöstrand framework to PYTHIA 8.130 with multiple Pomeron flux parameterizations and distinct low- and high-mass diffraction treatments using diffractive PDFs. The study compares PYTHIA with PHOJET, showing that incorporating hard diffraction improves p_T and multiplicity tails, aiding agreement with alternative models. It also highlights key uncertainties in Pomeron flux and cross-section, and outlines future enhancements, including central diffraction and extensive data validation.

Abstract

The PYTHIA program can be used to generate high-energy-physics 'events' with sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide a representation, as accurate as possible, of event properties in a wide range of reactions. One such reaction, that is not well understood is Diffraction. Among the several alternative approaches that have been proposed, in PYTHIA, we follow a fairly conventional Pomeron based one, but fully integrated to use the standard PYTHIA machinery for multiple interactions, parton showers and hadronization. This note reports the development in PYTHIA in the way diffraction is modeled without providing specific details for usage. Results are compared with an alternative event generator called PHOJET. The code and further information may be found on the Pythia web page: http://home.thep.lu.se/~torbjorn/Pythia.html.

Paper Structure

This paper contains 15 sections, 17 equations, 14 figures.

Table of Contents

  1. Diffraction and the Pomeron
  2. Classification
  3. Kinematics
  4. Diffraction in PYTHIA
  5. PYTHIA 6
  6. Event Generation
  7. Particle Production
  8. PYTHIA 6.214 vs PHOJET 1.12
  9. PYTHIA 8 before 8.130
  10. PYTHIA 8.130
  11. Event Generation
  12. Particle Production
  13. High-Mass Diffraction
  14. PYTHIA 8.130 vs PYTHIA 6.214 and PHOJET 1.12
  15. Conclusions and future outlook

Figures (14)

  • Figure 1: Diagram for elastic scattering and $\phi$ vs $\eta$ plot showing the distribution of products after the interaction.
  • Figure 2: SD diagram and a window showing a rapidity gap between $-10<\eta<3.5$.
  • Figure 3: DD diagram and window showing a rapidity gap between $-3.5<\eta<4$.
  • Figure 4: CD diagram and window showing two rapidity gaps between $-10<\eta<-2.5$ and $2.5<\eta<10$.
  • Figure 5: The diagram for an ND process. The rapidity window on the right shows that there is no rapidity gap.
  • ...and 9 more figures