EPOS LHC : test of collective hadronization with LHC data

TL;DR

EPOS LHC extends EPOS 1.99 by introducing a core–corona hadronization framework with a two-regime collective flow that depends on the total core mass. This approach describes LHC minimum-bias data across p-p, p-Pb, and Pb-Pb by combining string fragmentation in the corona with microcanonical core decay and flow, capturing enhanced strangeness and mass-dependent pT spectra. The model shows good agreement with cross-sections and bulk observables, and highlights the importance of final-state interactions even in small systems, while providing clear predictions for identified-particle R_pPb and multi-strange baryon production. Comparisons with PYTHIA underscore the value of including collective flow effects for soft QCD phenomena in high-energy hadron collisions.

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 LHC experiments have provided a number of very interesting data sets comprising minimum bias p-p, p-Pb and Pb-Pb interactions. We describe the changes required to the model to reproduce in detail the new data available from LHC and the consequences in the interpretation of these data. In particular we discuss the effect of the collective hadronization in p-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-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

Figures (34)

• Figure 1: Space time evolution of the particle production in an hadronic interaction. An hyperbola (line) represents particles with the same proper time. Figure a) is the standard approach for p-p scattering while figure b) is a more complete treatment used usually for HI collision.
• Figure 2: Elementary interaction in the EPOS model.
• Figure 3: Schematic view of the space time evolution of the particle production in an hadronic interaction in EPOS 1.99 or EPOS LHC. An hyperbola (line) represents particles with the same proper time. The same treatment is used for p-p or A-B but the collective hadronization, which can be local, is simplified compared to the full HI picture (done in EPOS 2 or 3).
• Figure 4: Fraction of charged particles with $|\eta|<2.4$ coming from the core as a function of the total number of charged particles with $|\eta|<2.4$. Solid line is used for simulation with EPOS at 7 TeV and dashed line for 900 GeV p-p scattering.
• Figure 5: Total, inelastic and elastic p-p cross section calculated with EPOS LHC (solid line) and EPOS 1.99 (dashed line). Points are data from PDG98 and the stars are the LHC measurements by the TOTEM experiment Csorgo:2012dm.