Abstract
Recent measurements at the LHC have revealed heavy-flavour baryon fractions much larger than those observed at LEP, with e.g., \( {\Lambda}_c^{+}/{\textrm{D}}^0 \) and \( {\Lambda}_b^0/{\textrm{B}}^0 \) reaching ∼ 0.5 at low p⊥. 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-p⊥ 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”.
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Acknowledgments
We are grateful to Gösta Gustafson and to Torbjörn Sjöstrand for many insightful discussions of the motion and fragmentation of junction string systems. We also thank the staff and students at the Rudolf Peierls Centre for Theoretical Physics in Oxford for a wonderful working environment during the completion of this work. This work was funded by the Australian Research Council via Discovery Project DP230103014 “Beautiful strings”, by the Royal Society Wolfson Visiting Fellowship “Piercing the precision barrier in high-energy particle physics”, and by the Monash-Warwick Alliance for Particle Physics. The work was also supported in part by the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 722105 — MCnetITN3.
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Altmann, J., Skands, P. String junctions revisited. J. High Energ. Phys. 2024, 238 (2024). https://doi.org/10.1007/JHEP07(2024)238
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DOI: https://doi.org/10.1007/JHEP07(2024)238