Angantyr – The Pythia 8 Heavy Ion model
Christian Bierlich, christian.bierlich@thep.lu.se
2
Heavy Ions in Pythia
- Heavy Ions in Pythia since v. 8.235.
- Extends default MPIs with nuclear geometry.
Main references:
CB, Gustafson, Lönnblad, Shah: 1806.10820 CB, Gustafson, Lönnblad: 1607.04434
3
Simulation tool for future upgrades
Focus on little/no tuning to heavy ion data.
Provides full, exclusive final states.
Simple extension, with all the Pythia features.
4
Demonstration
- Fully integrated with current Pythia workflow
- Support for several nuclei, more can be added by user.
- Written in C++, Python interface Exists, distributed with Pythia.
- Output formats:
HepMC, ROOT6 trees, Rivet
- Signal processes can be enabled, or read in from ME provider.
5
The model: Glauber
Built with inpiration from FRITIOF/Wounded
nucleons.
Glauber Monte Carlo, with focus on correct inclusion of diffraction pA is toy system of
choice.
6
The model: Glauber-Gribov fluctuations
Colour fluctuations parameterized.
Using perturbative
input (Mueller dipoles).
Log-normal or gamma- distribution.
7
Wounded nucleons
Białas and Czyz: Simple model for particle production.
Wounded nucleons contribute equally to multiplicity.
8
Wounded nucleons
Białas and Czyz: Simple model for particle production.
Wounded nucleons contribute equally to multiplicity.
9
Wounded nucleons
Białas and Czyz: Simple model for particle production.
Wounded nucleons contribute equally to multiplicity.
10
Wounded nucleons
Białas and Czyz: Simple model for particle production.
Wounded nucleons contribute equally to multiplicity.
11
The emission function
First two are normal collisions, second modelled as if single diffractive.
Generalizes to all pA and AA collisions.
12
Results (pA)
Delicate centrality measures well reproduced.
13
Multiplicity (pA)
14
Study model dep’t quantities
15
Spectra (pA)
16
Results (AA)
Centrality measures less important, but well reproduced.
17
Multiplicities well reproduced
18
Comparing to other models
19
Deficit at mid-rapidity
The deficit at mid-rapidity corresponds to Pythia pp deficit at low pT.
20
Impact parameter vs. centrality measure
Little bias in AA collisions.
21
PbPb spectra
22
RHIC energies (BRAHMS AuAu @ 200Gev)
Strangeness is one current object of interest.
“Rope model” implemented for pp, being extended.
23
Multiparticle correlations
24
Conclusion
Heavy ions are available in Pythia 8.
Useful for simulation studies for future detectors and upgrades.
Multiplicities and centrality measures well reproduced.
Collective effects from microscopic interactions is a work in progress.
