Thermodynamical String Fragmentation

TL;DR

This paper explores thermodynamic-inspired modifications to the Pythia event generator to better replicate heavy-ion-like phenomena in proton-proton collisions at the LHC, including transverse momentum generation, string environment effects, and rescattering.

Contribution

It introduces new thermodynamics-inspired models for string fragmentation, environment-dependent string tension, and hadron rescattering within Pythia, aiming to improve agreement with recent LHC data.

Findings

Some improvements in data description were observed.

Effects of modifications are complex and require further refinement.

Further work is needed to achieve significant impact.

Abstract

The observation of heavy-ion-like behaviour in pp collisions at the LHC suggests that more physics mechanisms are at play than traditionally assumed. The introduction e.g. of quark-gluon plasma or colour rope formation can describe several of the observations, but as of yet there is no established paradigm. In this article we study a few possible modifications to the Pythia event generator, which describes a wealth of data but fails for a number of recent observations. Firstly, we present a new model for generating the transverse momentum of hadrons during the string fragmentation process, inspired by thermodynamics, where heavier hadrons naturally are suppressed in rate but obtain a higher average transverse momentum. Secondly, close-packing of strings is taken into account by making the temperature or string tension environment-dependent. Thirdly, a simple model for hadron rescattering is added. The effect of these modifications is studied, individually and taken together, and compared with data mainly from the LHC. While some improvements can be noted, it turns out to be nontrivial to obtain effects as big as required, and further work is called for.