String junctions revisited

Abstract

Recent measurements at the LHC have revealed heavy-flavour baryon fractions much larger than those observed at LEP, with e.g., $$ {\Lambda}_c^{+}/{\textrm{D}}^0 $$ Λ c + / D 0 and $$ {\Lambda}_b^0/{\textrm{B}}^0 $$ Λ b 0 / 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”.