String Junctions Revisited

TL;DR

This paper revisits string junction models in QCD, especially for heavy-flavour baryon production at the LHC, proposing a new 'pearl on a string' scenario that improves understanding of heavy quark fragmentation.

Contribution

It introduces a novel 'pearl on a string' model for string junctions in the low-pT heavy quark limit, extending Pythia's fragmentation framework.

Findings

Enhanced agreement with LHC heavy-flavour baryon data

New theoretical insight into junction behavior with heavy quarks

Extended Pythia model for better simulation of baryon production

Abstract

Recent measurements at the LHC have revealed heavy-flavour baryon fractions much larger than those observed at LEP, with e.g., LambdaC+/D0 and LambdaB0/B0 reaching ~ 0.5 at low pT. One scenario that has been at least partly successful in predicting observed trends is QCD colour reconnections with string junctions. In previous work, however, the limit of a low-pT heavy quark was not well defined. We reconsider the string equations of motion for junction systems in this limit, and find that the junction effectively becomes bound to the heavy quark, a scenario we refer to as a "pearl on a string". We extend string-junction fragmentation in Pythia with a dedicated modelling of this limit for both light- and heavy-quark "pearls".