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Profile picture of Leif Lönnblad. Photo.

Leif Lönnblad

Professor of Theoretical Physics

Profile picture of Leif Lönnblad. Photo.

The Angantyr model for heavy-ion collisions in Pythia8


  • Christian Bierlich
  • Gösta Gustafson
  • Leif Lönnblad
  • Harsh Shah

Summary, in English

We present a new model for building up complete exclusive hadronic final states in high energy nucleus collisions. It is a direct extrapolation of high energy pp collisions (as described by Pythia), and thus bridges a large part of the existing gap between heavy ion and high energy physics phenomenology. The model is inspired by the old Fritiof model and the notion of wounded nucleons. Two essential features are the treatment of multi-parton interactions and diffractive excitation in each NN sub-collision. Diffractive excitation is related to fluctuations in the nucleon partonic sub-structure, and fluctuations in both projectile and target are here included for the first time. The model is able to give a good description of general final-state properties such as multiplicity and transverse momentum distributions, both in pA and AA collisions. The model can therefore serve as a baseline for understanding the non-collective background to observables sensitive to collective behaviour. As Pythia does not include a mechanism to reproduce the collective effects seen in pp collisions, such effects are also not reproduced by the present version of Angantyr. Effects of high string density, shown to be able to reproduce e.g. higher strangeness ratios and the ridge in pp, will be added in future studies.


  • Theoretical Particle Physics

Publishing year





Journal of High Energy Physics





Document type

Journal article




  • Subatomic Physics


  • Heavy Ion Phenomenology
  • Phenomenological Models




  • QCD Phenomenology and Event Generator Development
  • Innovative Network for Monte Carlo Event Generators for LHC Physics
  • Heavy-ion physics in Pythia


  • ISSN: 1029-8479