Hadron production in elementary nucleon-nucleon reactions from low to ultra-relativistic energies

TL;DR

This paper compares hadron production models in elementary nucleon-nucleon reactions across a wide energy range, highlighting the importance of accurate event generators for interpreting heavy-ion collision data.

Contribution

It provides a detailed comparison of PHSD and PYTHIA 8.2 models, including in-medium modifications and the role of QGP in high-energy collisions.

Findings

PHSD and PYTHIA models agree with experimental data across energies.

In-medium effects influence hadron multiplicities and distributions.

QGP formation impacts observables even in small systems at LHC energies.

Abstract

We study the hadron production in $p+p$, $p+n$ and $n+n$ reactions within the microscopic Parton-Hadron-Dynamics (PHSD) transport approach in comparison to PYTHIA 8.2. We discuss the details of the "PHSD tune" of the Lund string model (realized by event generators FRITIOF and PYTHIA) in the vacuum (as in $N+N$ collisions) as well as its in-medium modifications relevant for heavy-ion collisions where a hot and dense matter is produced. We compare the results of PHSD and PYTHIA 8.2 (default version) for the excitation function of hadron multiplicities as well as differential rapidity $y$, transverse momentum $p_T$ and $x_F$ distributions in $p+p$, $p+n$ and $n+n$ reactions with the existing experimental data in the energy range $\sqrt{s_{NN}} = 2.7 - 7000$ GeV. We discuss the production mechanisms of hadrons and the role of final state interactions (FSI) due to the hadronic rescattering. We also show the influence of the possible quark-gluon plasma (QGP) formation on hadronic observables in $p+p$ collisions at LHC energies. We stress the importance of developing a reliable event generator for elementary reactions from low to ultra-relativistic energies in view of actual and upcoming heavy-ion experiments.