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Abstract
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.
Highlights
At hadron collider experiments at RHIC and LHC, protons as well as large nuclei, are collided, and the results are interpreted to obtain better knowledge about the dynamics of the fundamental interactions at high energies
We present a new model for building up complete exclusive hadronic final states in high energy nucleus collisions
Since all parts of the simulation; GG colour fluctuations to generate the number of sub-collisions, the PYTHIA8 multi-parton interaction (MPI) model, the parton shower and the hadronisation model rely on a number of parameters, these parameters need to be tuned, and a large part of this paper describes how this procedure is carried out
Summary
At hadron collider experiments at RHIC and LHC, protons as well as large nuclei, are collided, and the results are interpreted to obtain better knowledge about the dynamics of the fundamental interactions at high energies. Exclusive final states in AA collisions, we have to calculate all sub-collisions between a nucleon μ in the projectile and nucleon ν in the target, study the number of multiple sub-interactions for all nucleons μ and ν, and here separate diffractive from non-diffractive (absorptive) interactions. Since all parts of the simulation; GG colour fluctuations to generate the number of sub-collisions, the PYTHIA8 MPI model, the parton shower and the hadronisation model rely on a number of parameters, these parameters need to be tuned, and a large part of this paper describes how this procedure is carried out.
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