EPOS LHC: Test of collective hadronization with data measured at the CERN Large Hadron Collider

TLDR

Epos is a Monte Carlo event generator for minimum‑bias hadronic interactions, used in heavy‑ion collisions and cosmic‑ray air‑shower simulations, and since its 2009 release the LHC has provided extensive minimum‑bias pp, p‑Pb, and Pb‑Pb data. The study details the model modifications needed to reproduce the new LHC data and discusses their implications for data interpretation. The updated model introduces a core–corona flow parametrization that depends only on collision geometry and secondary‑particle multiplicity, with distinct flow regimes for the small, high‑density core in pp collisions and the larger core in heavy‑ion collisions, enabling tests with p‑Pb data. Epos LHC successfully reproduces all minimum‑bias particle spectra from transverse momentum 0 to a few GeV/c.

Abstract

Epos is a Monte Carlo event generator for minimum bias hadronic interactions, used for both heavy ion interactions and cosmic ray air shower simulations. Since the last public release in 2009, the Large Hadron Collider (LHC) experiments have provided a number of very interesting data sets comprising minimum bias $p\text{\ensuremath{-}}p,\phantom{\rule{0.16em}{0ex}}p$-Pb, and Pb-Pb interactions. We describe the changes required to the model to reproduce in detail the new data available from the LHC and the consequences in the interpretation of these data. In particular we discuss the effect of the collective hadronization in $p\text{\ensuremath{-}}p$ scattering. A different parametrization of flow has been introduced in the case of a small volume with high density of thermalized matter (core) reached in $p\text{\ensuremath{-}}p$ compared to large volume produced in heavy ion collisions. Both parametrizations depend only on the geometry and the amount of secondary particles entering in the core and not on the beam mass or energy. The transition between the two flow regimes can be tested with $p$-Pb data. Epos LHC is able to reproduce all minimum bias results for all particles with transverse momentum from ${p}_{\mathrm{t}}=0$ to a few GeV/$c$.